What is the difference between A325 and A490 bolts in structural steel?

A325 and A490 bolts are the two primary high-strength bolt grades for structural steel connections, both now covered under ASTM F3125 (which consolidated A325, A325M, A490, A490M, F1852, and F2280 into a single specification). The fundamental differences are: (1) Material strength: A325 (Group A) bolts have a minimum tensile strength Fu = 120 ksi. A490 (Group B) bolts have Fu = 150 ksi — 25% stronger. (2) Shear strength per AISC 360 Table J3.2: For a 3/4 inch bolt with threads excluded from the shear plane (X condition), A325-X provides 22.5 kip shear capacity (phi = 0.75) while A490-X provides 27.9 kip — a 24% increase. For threads included (N condition), A325-N = 17.9 kip and A490-N = 22.5 kip. (3) Tensile strength: Both grades have the same tensile strength for a given diameter because Fnt differs: 90 ksi for A325, 113 ksi for A490 — but phi*Fnt*Ab yields 29.8 kip for both at 3/4 inch diameter because AISC caps the tensile design strength at the pretension level. (4) Minimum pretension: A490 requires 25% higher pretension than A325 for the same diameter (3/4 inch: 28 kip for A325 vs 35 kip for A490). (5) Material and application restrictions: A490 bolts are made from alloy steel and are not permitted in painted or galvanized faying surfaces for slip-critical connections (RCSC Section 2.4), because the lubricating effect of coatings reduces the slip coefficient and A490 requires the highest possible slip resistance. A490 is also not permitted in connections subject to significant prying or fatigue unless specifically qualified. A325 is more commonly specified (approximately 80% of structural bolts are A325), with A490 reserved for heavily loaded connections where the strength premium justifies the cost premium (10-15% more for A490). For a typical beam end-plate connection, moving from A325-X to A490-X bolts can reduce the number of bolts by about 20%, which may reduce connection fabrication cost despite the higher per-bolt cost. Group C (F3043) bolts offer an even higher strength tier with Fu = 170 ksi.

What does threads included (N) vs threads excluded (X) mean for bolt shear?

The N vs X designation in AISC 360 Table J3.2 refers to whether the threaded portion of the bolt shank falls within the shear plane of the connection. Threads included in the shear plane (Condition N) means the shear plane passes through the threaded region where the bolt cross-sectional area is reduced to the tensile stress area (about 75-80% of the nominal area). This is the default design assumption and produces a lower shear capacity. Threads excluded from the shear plane (Condition X) means the shear plane passes through the unthreaded shank where the full nominal bolt area is available, producing about 20-25% higher shear capacity. N vs X is NOT about whether the bolt has threads — all bolts have threads. It is about WHERE the threads are relative to the shear plane, which depends on the grip length (total thickness of plies being connected) and the bolt length specified. For a standard A325 3/4 inch bolt: single shear capacity (phi = 0.75) is 17.9 kip for N and 22.5 kip for X — a 26% difference. For A490 3/4 inch: 22.5 kip (N) vs 27.9 kip (X) — a 24% difference. In practice: for typical beam end-plate connections with 3/8-3/4 inch shear tab or end plate thickness, the grip is short and threads are often in the shear plane (N condition). For column splice connections with 2-3 inch grip lengths, threads can be excluded (X condition) by specifying a longer bolt with an unthreaded shank length that corresponds to the location of the shear planes. The RCSC Specification provides guidance on bolt length selection: the bolt length should be such that at least one or two full threads project beyond the nut after tightening (the stick-through requirement), which gives a grip range for each bolt length. Specifying X condition requires the engineer to verify that the thread run-out (the transition from full threads to unthreaded shank) does not fall within the shear plane — this verification should be noted on the design drawings. In many practical cases, engineers conservatively assume N condition (threads included) to avoid the risk of the thread run-out falling in the shear plane due to grip length tolerances, at the cost of slightly more bolts.

When are slip-critical connections required instead of bearing-type?

Slip-critical (SC) connections, also called friction-type connections, are required when slip at the bolted joint would impair the serviceability or structural performance of the connection. The RCSC Specification and AISC 360 Section J3.8 mandate slip-critical connections for: (1) Connections subject to fatigue loading or load reversal (cyclic loads), including crane runway girders, machinery supports, and bridge stringers. Slip in a bearing connection under load reversal would cause progressive hole elongation and eventual failure. (2) Connections with oversize holes (d_hole > d_bolt + 1/16 inch standard) or slotted holes in the direction of loading — the larger hole allows movement that must be prevented by clamping force. (3) Connections where slip would cause excessive deformation in the structure — for example, connections at the top of tall slender columns where drift amplification occurs, or connections in moment frames where slip would change the frame stiffness (and therefore the moment distribution). (4) Column splices subject to net tension (uplift or cantilever columns), where slip would cause separation at the splice. Column splices in compression only can be bearing-type with snug-tight bolts. (5) Connections in SCBF or BRBF where the bolt group carries seismic forces — slip under earthquake loading compromises the system ductility and energy dissipation. (6) Hybrid connections that combine welds and bolts where the bolts share load with welds. The slip-critical design shear capacity is: phi * mu * D_u * h_f * T_b * n_s where mu = mean slip coefficient (typically 0.30 for Class A surface — clean mill scale, 0.50 for Class B — blast-cleaned), D_u = 1.13 (ratio of mean to minimum pretension), h_f = 1.00 for standard holes (filler factor), T_b = minimum bolt pretension, and n_s = number of slip planes. For an A325 3/4 inch bolt with Class A faying surface (mu = 0.30), the slip-critical capacity per bolt is 0.30 * 1.13 * 1.00 * 28 * 1 = 9.5 kip (at service load level, phi = 1.0 for serviceability). This is substantially lower than the bearing-type shear capacity of 17.9 kip, meaning SC connections require approximately twice as many bolts, or larger diameter bolts, for the same applied load.

How do you check bolts for combined shear and tension?

Many structural connections subject bolts to combined shear and tension simultaneously — for example, beam end-plate moment connections where the top bolts resist tension from the applied moment while all bolts resist shear. AISC 360-22 Section J3.7 provides the interaction equation for combined shear and tension in bearing-type connections. When the required shear stress f_rv = V_u / A_b produces a tensile stress reduction, the available tensile strength is reduced. The interaction equation (Eq. J3-3a for LRFD): f_rv must be less than or equal to phi * F'_nt, where F'_nt is the reduced nominal tensile strength accounting for shear. F'_nt is calculated as: F'_nt = 1.3 * F_nt - (F_nt / (phi * F_nv)) * f_rv, but not greater than F_nt. The factor (F_nt / (phi * F_nv)) = 90 / (0.75 * 54) = 2.22 for A325-N bolts. For each kip per square inch of applied shear stress, the tensile capacity drops by 2.22 ksi. Example: a 3/4 inch A325-N bolt has A_b = 0.442 in^2, F_nt = 90 ksi, F_nv = 54 ksi. If this bolt is loaded with 5 kip shear (f_rv = 11.3 ksi), then F'_nt = 1.3 * 90 - 2.22 * 11.3 = 117 - 25.1 = 91.9 ksi, capped at 90 ksi — so no reduction. At 10 kip shear (f_rv = 22.6 ksi), F'_nt = 117 - 50.2 = 66.8 ksi, a 26% reduction in tensile capacity. At 15 kip shear (f_rv = 33.9 ksi), F'_nt = 117 - 75.3 = 41.7 ksi, a 54% reduction. The interaction is severe at high shear levels because the von Mises yield criterion governs combined stress. A common design approach: separate shear and tension load paths where possible. For example, in a typical bolted moment end-plate connection, provide a separate shear tab or bearing plate to carry the beam shear, leaving the end-plate bolts to carry only tension from the moment. If shear and tension must share the same bolts, the interaction check often governs the bolt group capacity and may require larger or more bolts than either shear or tension alone would demand. For slip-critical connections, the bolt pretension provides the clamping force that resists shear via friction, and the interaction is checked differently — the reduced slip resistance accounts for tension reducing the clamping force: the available slip resistance is reduced by the factor (1 - T_u / (1.13 * T_b)) to account for tension demand reducing the effective clamping.

What is the difference between snug-tight and pretensioned bolt installation?

Snug-tight and pretensioned are the two installation methods for high-strength bolts, and the choice affects connection behavior, cost, and inspection requirements. Snug-tight is the minimum required installation for all bolted connections per RCSC Specification Section 8.1. A snug-tight bolt is defined as the tightness attained by the full effort of a worker using an ordinary spud wrench (no extension), or a few impacts of an impact wrench. There is no specific tension value to verify — the bolt is simply tightened until the plies are in firm contact and the bolt will not loosen under handling. Snug-tight connections are permitted for: all bearing-type connections in static loading, connections not subject to fatigue or vibration, and most standard beam-to-column and beam-to-girder shear connections (shear tabs, double angles, single-plate shear connections). Snug-tight is the default for approximately 85-90% of structural connections. Pretensioned installation requires the bolt to be tightened to a minimum tension equal to 70% of the bolt tensile strength (0.70 * F_u * A_b). For A325 3/4 inch, the minimum pretension is 28 kip. Pretensioned bolts must be installed using one of four approved methods per RCSC Section 8.2: (1) Turn-of-nut method — tighten to snug-tight, then apply a specified rotation (1/3 turn for bolt length up to 4x diameter, 1/2 turn for 4-8x diameter, 2/3 turn for 8-12x). This is the most common method. (2) Calibrated wrench method — use a torque wrench calibrated to produce the required tension on a representative sample of bolts from the same lot. (3) Twist-off-type tension-control bolts (TC bolts or F1852) — the splined end shears off at a factory-calibrated torque corresponding to the minimum pretension, providing direct visual inspection. (4) Direct tension indicator (DTI) washers — the protrusions on the DTI washer are compressed until a feeler gage cannot enter the gap, indicating the required tension has been achieved. Pretensioned bolts are required for: slip-critical connections, connections subject to fatigue or significant load reversal, column splices with tension, A490 bolts in tension (to prevent prying relaxation), and connections where bolt loosening would be catastrophic (e.g., crane supports). Pretensioning adds cost: TC bolts cost 20-30% more than standard A325 bolts, and calibrated wrench or DTI installation requires additional inspection time. The engineer should specify pretensioned installation only when functionally required, not as a blanket requirement.

Steel Fasteners — Bolt Grades, Design Strengths, and Installation

Structural steel fasteners include high-strength bolts (A325/F3125 Grade A325, A490/F3125 Grade A490), common bolts (A307), and specialty fasteners (tension-control bolts, lockbolts, self-drilling screws). AISC 360-22 Chapter J and the RCSC Specification for Structural Joints govern bolt design and installation. The correct selection of fastener grade, installation method, and connection type directly affects connection capacity and structural performance.

Bolt grades and design strengths (AISC 360-22 Table J3.2)

Grade	ASTM	Fnv N/X (ksi)	Fnt (ksi)	Fu (ksi)	Common Sizes
Group A (A325)	F3125 Gr. A325	54 / 68	90	120	3/4", 7/8", 1"
Group B (A490)	F3125 Gr. A490	68 / 84	113	150	3/4", 7/8", 1"
Group C (F3043)	F3043	77 / 96	113	170	3/4", 7/8", 1"
A307 Grade A	A307	27	45	60	1/2" to 1-1/2"
A307 Grade B	A307	27	45	60	1/4" to 4"

N vs X: N = threads included in the shear plane (default assumption, lower capacity). X = threads excluded from the shear plane (higher capacity, but requires careful detailing to ensure threads are not in the shear plane).

Complete bolt capacity table — single shear, phi = 0.75

Diameter	Ab (in^2)	A307-N (kip)	A325-N (kip)	A325-X (kip)	A490-N (kip)	A490-X (kip)
1/2"	0.1963	4.0	8.0	10.0	10.0	12.4
5/8"	0.3068	6.2	12.4	15.7	15.7	19.4
3/4"	0.4418	8.9	17.9	22.5	22.5	27.9
7/8"	0.6013	12.2	24.3	30.7	30.7	37.9
1.0"	0.7854	15.9	31.8	40.1	40.1	49.7
1-1/8"	0.9940	20.1	40.3	50.7	50.7	62.7

Double shear capacity (both shear planes active)

Diameter	A325-N double (kip)	A325-X double (kip)	A490-N double (kip)	A490-X double (kip)
3/4"	35.8	45.1	45.1	55.7
7/8"	48.7	61.3	61.3	75.8
1.0"	63.7	80.1	80.1	99.3
1-1/8"	80.5	101.4	101.4	125.3

Double shear = 2x single shear. Double-shear connections (double angles, end plates) are significantly more efficient per bolt.

Bolt tension capacity — phi = 0.75

Diameter	A325 phiTn (kip)	A490 phiTn (kip)	Min. Pretension A325 (kip)	Min. Pretension A490 (kip)
1/2"	13.2	13.2	12	15
5/8"	20.7	20.7	19	24
3/4"	29.8	29.8	28	35
7/8"	40.6	40.6	39	49
1.0"	53.0	53.0	51	64
1-1/8"	67.1	67.1	56	71

phiTn = 0.75 * Fnt * Ab. Fnt = 90 ksi (A325) or 113 ksi (A490). Min pretension = 0.70 * Fu * Ab.

Installation methods

Snug-tight (AISC 360 Section J3.1)

Bolts tightened to the "snug-tight" condition -- full effort of a single worker with an ordinary spud wrench, or a few impacts of an impact wrench. This is the minimum installation requirement and is permitted for:

Bearing-type connections in static loading
Connections not subject to fatigue, vibration, or load reversal
Non-slip-critical applications

Pretensioned (Section J3.1, Table J3.1)

Bolts tightened to a minimum tension equal to 70% of the bolt tensile strength. Required for:

Slip-critical connections
Connections subject to fatigue
Column splices with tensile loads
Connections to bracing members
A490 bolts subject to tension (to prevent prying relaxation)

Pretensioning methods (RCSC Specification)

Method	Equipment	Reliability	Speed	Notes
Turn-of-nut	Standard wrench	High	Moderate	1/3 to 1 full turn after snug-tight
Calibrated wrench	Torque wrench (calibrated daily)	Moderate	Slow	Requires daily calibration
Twist-off (TC bolt)	Special spline gun	High	Fast	Most common modern method
Direct tension (DTI)	DTI washer	High	Moderate	Protrusions flatten at required tension

Turn-of-nut rotation requirements (RCSC Table 8.2)

Bolt Length	Both Faces Normal	One Face Normal, Other Beveled	Both Faces Beveled
Up to 4 diameters	1/3 turn	1/2 turn	2/3 turn
4 to 8 diameters	1/2 turn	2/3 turn	5/6 turn
8 to 12 diameters	2/3 turn	5/6 turn	1 turn

Slip-critical connections (Section J3.8)

Slip-critical connections resist loads by friction between faying surfaces, not bolt bearing:

phiRn = mu * Du * hf * Tb * ns    [per bolt]
phi = 1.00 (serviceability) or 0.85 (strength)

Where mu = slip coefficient (Class A = 0.30, Class B = 0.50), Du = 1.13, hf = filler factor, Tb = bolt pretension, ns = number of slip planes.

Slip resistance per bolt — single slip plane (phi = 0.85)

Diameter	Tb A325 (kip)	Class A (kip)	Class B (kip)	Class A A490 (kip)	Class B A490 (kip)
3/4"	28	8.1	13.5	10.1	16.8
7/8"	39	11.3	18.8	14.1	23.4
1.0"	51	14.7	24.6	18.4	30.6
1-1/8"	56	16.2	27.0	20.2	33.6

Class B surfaces (blast-cleaned) provide 67% higher slip resistance than Class A (mill scale).

When slip-critical is required

Condition	Required?
Bearing-type, static loading	No
Joints with oversized/long-slotted holes	Yes
Connections subject to fatigue	Yes
Connections with load reversal	Yes
Column splices in tension	Yes
Bracing connections (some jurisdictions)	Yes
A490 bolts in tension (prying)	Yes

Combined shear and tension (Section J3.7)

When bolts carry both shear and tension simultaneously:

F'nt = 1.3*Fnt - (Fnt/(phi*Fnv))*frv <= Fnt

Where frv = required shear stress per bolt. This equation linearly reduces the available tensile strength as shear demand increases.

Combined interaction example — A325-N, 3/4" bolt

frv (ksi)	F'nt (ksi)	Available Tension (kip)	% Tension Remaining
0	90.0	29.8	100%
10	67.8	22.4	75%
20	45.6	15.1	51%
30	23.3	7.7	26%
40.5	0	0	0% (full shear)

At frv = 40.5 ksi (= Fnv = 54 ksi * 0.75), all capacity is consumed by shear and no tension is available.

Specialty fasteners

Tension-control (TC) bolts

F3125 Grade A325 TC and F3125 Grade A490 TC are the most commonly specified modern high-strength bolts. The splined tip shears off at the required pretension, providing visual verification of proper installation. No torque calibration is needed.

Lockbolts (Huck bolts)

Collar-swaged fasteners that cannot be loosened once installed. Used in bridge, industrial, and modular construction. Not covered by AISC, but many DOTs accept them.

Self-drilling screws (AISI S100)

For cold-formed steel connections per AISI S100. Typical pullout and shear values:

Screw Size	Washer Dia (in)	Pullout 14ga (kip)	Shear 14ga (kip)
#10	0.375	0.19	0.17
#12	0.375	0.22	0.20
1/4"	0.500	0.31	0.26

Structural rivets

Historically common but now rarely used. Replaced by high-strength bolts and welding. A502 Grade 1 (Fr = 18 ksi) and Grade 2 (Fr = 24 ksi). Still encountered in renovation of pre-1960 structures.

Multi-code comparison

Code	A325 Equivalent	A490 Equivalent	phi (shear)	phi (tension)
AISC 360	F3125 Gr. A325	F3125 Gr. A490	0.75	0.75
AS 4100	AS/NZS 1252 Gr 8.8	AS/NZS 1252 Gr 10.9	0.80	0.80
EN 1993-1-8	Class 8.8	Class 10.9	gamma_M2=1.25	gamma_M2=1.25
CSA S16	ASTM A325	ASTM A490	0.80	0.80

Shear capacity comparison — 3/4" bolt, single shear

Code	A325 Equivalent (kip)	A490 Equivalent (kip)
AISC 360 (N)	17.9	22.5
AS 4100	20.5	25.7
EN 1993-1-8	17.8	22.3
CSA S16	20.1	25.3

AS 4100 and CSA S16 use phi = 0.80 vs AISC's 0.75, giving ~12% higher capacity.

Common mistakes

Assuming threads excluded (X) without verifying. The default is threads included (N). Threads-excluded capacity requires controlling thread length and stick-through, which is often impractical.
Using A490 bolts in galvanized connections. A490 bolts must not be galvanized due to hydrogen embrittlement risk. Use A325 (galvanizable) or F3125 Grade A354 Grade BD (galvanizable alternative).
Not checking bearing and tearout. Bolt shear capacity is an upper bound. If the connected plate is thin, bearing or tearout at bolt holes may govern at a lower load.
Specifying slip-critical when not required. Slip-critical connections cost more due to surface preparation and pretensioning requirements. Use bearing-type connections for static loading when code permits.
Forgetting the 0.75 resistance factor. Bolt design uses phi = 0.75, not 0.90. This is frequently confused with member design resistance factors.
Mixing bolt grades on the same project. Creates installation confusion and the risk of under-tensioning A490 bolts or breaking A325 bolts.
Using A307 bolts for structural connections. A307 (Fnv = 27 ksi) has less than half the shear capacity of A325 (Fnv = 54 ksi). Generally only used for non-structural or lightly loaded connections.

Frequently asked questions

What is the most commonly used structural bolt? 3/4" A325-N (F3125 Grade A325), snug-tight, bearing-type. This covers the majority of simple shear connections in building construction.

When do I need slip-critical connections? When the connection uses oversized or slotted holes, is subject to fatigue or load reversal, or when the specification requires it. For standard round holes with static loads, bearing-type is sufficient.

What is the difference between A325 and A490? A490 has 26% higher shear strength (68 ksi vs 54 ksi Fnv for N-type) and 26% higher tensile strength (113 ksi vs 90 ksi Fnt). A490 costs ~30-50% more and cannot be galvanized.

How do I know if threads are excluded? Threads are excluded when the grip length (total thickness of connected material) exceeds the bolt's thread length. For standard A325 bolts, the thread length is approximately 2d + 1/4". If the grip is longer than this, threads will be excluded from the shear plane.

Can I reuse A325 bolts? AISC permits reuse of A325 bolts at the engineer's discretion if they can be tightened to the snug-tight condition. A490 bolts should not be reused. TC bolts (twist-off) cannot be reused.

What about stainless steel bolts? Stainless steel bolts (ASTM A193 B8, A320 B8) are used in corrosive environments. They have lower strength (Fnv ~ 20-30 ksi) and different installation requirements. Not common in building construction.

Run this calculation

ASTM F3125 Bolt Specifications

ASTM F3125 is the consolidated standard that covers high-strength structural bolts previously specified under separate standards (A325, A490, A325M, A490M). Adopted in 2015, it simplifies procurement and specification by placing all high-strength bolt grades under one standard with different grades and types.

ASTM F3125 Grade	Former Standard	Min. Tensile (ksi)	Min. Yield (ksi)	Proof Load (ksi)	Diameter Range	Typical Finish
Grade A325 (Type 1)	ASTM A325	120	92	85	1/2" – 1-1/2"	Black or galvanized
Grade A325 (Type 3)	ASTM A325	120	92	85	1/2" – 1-1/2"	Weathering (Corten)
Grade A490 (Type 1)	ASTM A490	150	130	120	1/2" – 1-1/2"	Black only
Grade A490 (Type 3)	ASTM A490	150	130	120	1/2" – 1-1/2"	Weathering (Corten)
Grade F3125 (Grade A325M)	A325M metric	830 MPa	660 MPa	—	M16–M36	Black or galvanized
Grade F3125 (Grade A490M)	A490M metric	1040 MPa	935 MPa	—	M16–M36	Black only

A325 vs A490 Detailed Comparison

Understanding the differences between A325 and A490 bolts is critical for proper connection design. While both are high-strength structural bolts, their mechanical properties and limitations differ significantly.

Property	A325	A490
Min. tensile strength	120 ksi	150 ksi
Min. yield strength	92 ksi	130 ksi
Shear strength (LRFD)	54 ksi (threads excluded), 68 ksi (threads included) per bolt × Ab	68 ksi (threads excluded), 84 ksi (threads included) per bolt × Ab
Allowable galvanizing	Yes (hot-dip or mechanical)	No — hydrogen embrittlement risk
Cost premium	Baseline	40–60% more expensive
Nut specification	ASTM A563 Grade C or DH	ASTM A563 Grade DH or DH3
Washer requirement	Hardened washer per ASTM F436	Hardened washer mandatory (F436)
Pre-installation verification	RCSC Section 7	RCSC Section 7 (mandatory)
Typical diameter	3/4", 7/8", 1"	7/8", 1", 1-1/8"
Corrosion resistance	Type 3 available for weathering steel	Type 3 available for weathering steel

When to use A325: Most building connections, standard shear and tension applications, galvanized connections, and cost-sensitive projects.

When to use A490: High-demand connections requiring fewer bolts, tension-critical joints such as flange connections in moment frames, heavy column splices, and connections with limited geometry that demand higher per-bolt capacity.

Washer Requirements per RCSC

Washers serve multiple functions in bolted joints: distributing clamp force, preventing gouging of connected material, providing a bearing surface for nut rotation, and indicating pretension in twist-off type bolts.

Condition	Washer Type	Standard	Quantity
A325, bearing-type, standard holes	Not required (but recommended)	—	—
A325, bearing-type, oversized/short-slotted holes	Hardened washer	ASTM F436	Under nut or bolt head (one side)
A325, bearing-type, long-slotted holes	Hardened washer + plate washer	ASTM F436	Both sides
A325, slip-critical	Hardened washer	ASTM F436	Under turning element
A490, all conditions	Hardened washer	ASTM F436	Under turning element (mandatory)
A490, oversized or slotted holes	Hardened washer + plate washer	ASTM F436	Both sides
Twist-off (TC) bolts	Special installation washer	Per manufacturer	Under spline end
Galvanized A325	Hardened washer (galvanized or plain)	ASTM F436	Under nut
Faying surface preparation	No washer required (paint/coating is the issue)	—	—

Bolt Installation Methods per RCSC

The Research Council on Structural Connections (RCSC) Specification defines four accepted pretensioning methods for slip-critical and pretensioned connections. Bearing-type connections do not require specific pretensioning beyond the snug-tight condition.

Method	Description	Equipment Required	Verification	Best Application
Turn-of-nut	Rotate nut a specified number of turns from snug-tight	Wrench or ratchet	Inspection by rotation mark	Most common field method
Twist-off (TC) bolt	Spline shears off at design pretension	Special TC wrench	Visual — spline tip separated	Rapid field installation
Direct tension indicator (DTI)	Compressible washer with protrusions that flatten	Wrench + DTI feeler gauge	Feeler gauge gap check	Reliable verification, inspectable
Calibrated wrench	Torque wrench calibrated to bolt pretension	Calibrated torque wrench	Calibration certificate	Shop conditions, controlled environment

Snug-tight condition: All plies in firm contact. Achieved with a few impacts of an impact wrench or full manual effort with a spud wrench. Required minimum for all bearing-type connections.

Pretensioned condition: Specific minimum tension achieved per RCSC Table 5.2 (e.g., 28 kips for 3/4" A325, 49 kips for 1" A490). Required for slip-critical joints, joints subject to fatigue, and A490 bolts in tension.

Inspection Requirements per RCSC

Bolt inspection is a critical quality assurance step. The level of inspection depends on the connection type and the installation method used.

Inspection Type	When Required	What to Verify
Visual (all connections)	All bolted connections	Bolt grade marking, correct diameter, faying surface condition, hole size and type
Snug-tight verification	Bearing-type connections	Firm contact of all plies, no gaps
Turn-of-nut inspection	Pretensioned or slip-critical	Match marks after rotation; rotation matches specification
TC bolt visual	Pretensioned or slip-critical	Spline tip completely separated from bolt shank
DTI feeler gauge	Pretensioned or slip-critical	Feeler gauge refusal at specified gap
Calibrated wrench	Pretensioned or slip-critical	Calibration documentation, torque values
Slip-critical faying surface	All slip-critical connections	Surface preparation, paint system, slip coefficient
Magnetic particle or UT	A490 tension members (engineer-specified)	No hydrogen embrittlement cracking

Related references

Disclaimer

This page is for educational and reference use only. It does not constitute professional engineering advice. All design values must be verified against AISC 360-22 Chapter J and the RCSC Specification. The site operator disclaims liability for any loss arising from the use of this information.

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