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- PED 2014/68/EC
- NACE MR0175/ISO 15156-2
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- MERKBLATT AD 2000 W2/W7/W10
F436 Washer + A325/A490 Tightening Torque Chart - RCSC Calculated Values
F436 hardened steel washers are installed under the turned element (typically the nut) of A325, A490 and F3125 high-strength structural bolts to preserve preload through service. The torque values below are calculated per the short-form equation T = K x F x D, with the target preload F set at 70% of minimum specified tensile strength per RCSC Specification Table 8.1. Sizes covered: 1/2 in through 1 1/2 in UNC for both A325 (120 ksi UTS) and A490 (150 ksi UTS) with F436 hardened washer under the turned nut.
Torque calculation basis
The short-form torque-tension relationship is T = K x F x D where T is installation torque (inch-pound), K is the empirical nut factor (0.13 typical for nickel-anti-seize lubricated F3125 bolt + F436 washer + A563 hex nut), F is target preload (pound-force), and D is nominal bolt diameter (inch). Target preload per RCSC Table 8.1 is 70% of the specified minimum tensile strength multiplied by the ASME B1.1 tensile stress area. Below 1/2 in. the bolt is not a structural HSFG bolt; above 1 1/2 in. A325 large-diameter heavy hex (A325 type 1 or 3) follows the same table.
A325 (120 ksi UTS) + F436 + A563 — torque chart
| Size UNC | D (in) | As (in²) | Min preload F (lbf) | T anti-seize K=0.13 (ft·lb) | T PTFE K=0.11 (ft·lb) |
|---|---|---|---|---|---|
| 1/2-13 | 0.500 | 0.1419 | 12,000 | 65 | 55 |
| 5/8-11 | 0.625 | 0.2260 | 19,000 | 129 | 109 |
| 3/4-10 | 0.750 | 0.3340 | 28,000 | 228 | 193 |
| 7/8-9 | 0.875 | 0.4620 | 39,000 | 370 | 313 |
| 1-8 | 1.000 | 0.6060 | 51,000 | 553 | 468 |
| 1 1/8-7 | 1.125 | 0.7630 | 56,000 | 683 | 578 |
| 1 1/4-7 | 1.250 | 0.9690 | 71,000 | 962 | 814 |
| 1 3/8-6 | 1.375 | 1.1550 | 85,000 | 1,266 | 1,071 |
| 1 1/2-6 | 1.500 | 1.4050 | 103,000 | 1,674 | 1,416 |
A490 (150 ksi UTS) + F436 + A563 — torque chart
A490 develops higher preload than A325 of the same diameter. RCSC Table 8.1 lists A490 minimum preload at 70 percent of 150 ksi specified minimum tensile. F436 hardened washer is mandatory under the turned element to avoid brinelling.
| Size UNC | D (in) | As (in²) | Min preload F (lbf) | T anti-seize K=0.13 (ft·lb) | T PTFE K=0.11 (ft·lb) |
|---|---|---|---|---|---|
| 1/2-13 | 0.500 | 0.1419 | 15,000 | 81 | 69 |
| 5/8-11 | 0.625 | 0.2260 | 24,000 | 163 | 138 |
| 3/4-10 | 0.750 | 0.3340 | 35,000 | 285 | 241 |
| 7/8-9 | 0.875 | 0.4620 | 49,000 | 465 | 393 |
| 1-8 | 1.000 | 0.6060 | 64,000 | 694 | 587 |
| 1 1/8-7 | 1.125 | 0.7630 | 80,000 | 975 | 825 |
| 1 1/4-7 | 1.250 | 0.9690 | 102,000 | 1,381 | 1,169 |
| 1 3/8-6 | 1.375 | 1.1550 | 121,000 | 1,801 | 1,524 |
| 1 1/2-6 | 1.500 | 1.4050 | 148,000 | 2,405 | 2,035 |
RCSC pretensioning methods
| Method | Procedure | F436 washer placement |
|---|---|---|
| Turn-of-Nut | Snug-tight then rotate nut a specified additional turn per RCSC Table 8.2 (1/3 to 1 turn depending on bolt length) | F436 under the turned element (typically nut) |
| Calibrated Wrench | Use torque values from the chart above, calibrated to a tension calibrator (Skidmore-Wilhelm) at the start of each shift | F436 under the turned element |
| Twist-Off (F1852 / F2280) | Spline pulls free when target preload reached; no torque measurement | F436 under nut on the non-spline end only |
| Direct Tension Indicator | DTI compresses to a calibrated gap when target reached | F436 between DTI and structural member where required |
Where to place the F436 washer
RCSC Specification Section 6.1 places the hardened washer under the turned element. For most structural connections this is the nut, which means F436 sits between the nut bearing face and the connected structural member. If the bolt is turned (head rotated during installation), the washer goes under the bolt head instead. In slotted-hole connections, an F436 washer is required on both faces. In oversized-hole connections, the F436 must be the extra-thick variant per F436 Note B. For full F436 hardware planning across the joint, see F436 washer specifications.
Cross-references
Mating bolt standards: F436 vs F844 (when not to use the cheaper non-hardened F844), F436 vs SAE (SAE J476 / J996 comparison), F436 vs Grade 8 (SAE Grade 8 washer comparison). For metric torque charts use F436M metric washers with A325M / A490M bolting (same RCSC Table 8.1 percentages, metric tensile stress areas from ISO 898-1).
Frequently asked questions
How do I calculate F436 + A325 torque?
Use T = K x F x D where T is in inch-pound, K is 0.13 for anti-seize-lubricated F3125 bolt + F436 washer + A563 nut, F is the RCSC Table 8.1 minimum preload (70 percent of bolt minimum tensile strength times tensile stress area), and D is nominal bolt diameter in inches. Divide by 12 to convert to foot-pound. Worked example for 1 in. A325: F = 51,000 lbf, T = 0.13 x 51,000 x 1.0 = 6,630 in-lb = 553 ft-lb. Always verify the calibrated wrench against a Skidmore-Wilhelm tension calibrator at the start of each shift.
Does the F436 washer change the torque value?
The F436 hardened washer is included in the K value calibration assumed by RCSC Table 8.1. A test that calibrates the wrench against a Skidmore-Wilhelm with the SAME bolt-washer-nut assembly that will be used in the field automatically captures the F436 contribution. Substituting a soft F844 or DIN 125 washer for F436 reduces installed preload by 5 to 15 percent (washer creep absorbs preload) and is not RCSC-compliant. The torque value does not change, but the resulting preload does — that is why F436 is mandatory.
When do I use the extra-thick F436?
RCSC Specification requires the F436 extra-thick variant (nominal 5/16 in. thickness) when the connection has oversized holes or short-slotted holes. The extra-thick washer spreads the bearing pressure over a larger area and prevents the bolt head or nut from rotating into the oversized hole during tightening. For standard-hole connections, the standard F436 thickness (0.097 to 0.177 in. depending on size) is sufficient. See the dim table at F436 washer dimensions.
What lubricant gives K = 0.13?
K = 0.13 is published in RCSC Specification Commentary as the nominal nut factor for new black-oxide A325 or A490 bolts with anti-seize compound on the threads and the bearing face of the turned element. Typical anti-seize products that deliver K in the 0.125 to 0.135 band are Jet-Lube SS-30, Loctite C5-A, Bostik Never-Seez, and Permatex 80078 nickel anti-seize. Dry as-received bolts run K = 0.20 to 0.30 with high scatter and are not acceptable for calibrated-wrench installation; use turn-of-nut instead, or lubricate the assembly to a known K value before torque-based installation.
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