Bolt Proof, Yield, and Tensile Load (SAE J429)

Strength acts on the tensile stress area At = 0.7854 x (D - 0.9743/n)^2 (about 15% under the nominal shank, so a nominal-area guess over-predicts), and the grade -- read from the head markings -- sets every number. A 1/2-13 Grade 5 bolt (At 0.1419 in^2) has a 12,060 lb proof load, 17,030 lb tensile, and a 9,045 lb recommended clamp (75% of proof); the identical bolt in Grade 8 jumps to 17,028 lb proof and 12,771 lb clamp. Grade 2: 55/57/74 ksi; Grade 5 / A325: 85/92/120; Grade 8 / A490: 120/130/150. A design aid; the joint design, torque method, and preload requirement govern.

At = 0.7854 x (D - 0.9743/n)^2; proof_load = At x proof_strength; yield_load = At x yield_strength; tensile_load = At x tensile_strength; rec_clamp = 0.75 x proof_load.

The SAE J429 inch-series bolt strength model (tensile stress area x grade strength), with the ASME B1.1 tensile stress area, by name; the joint design, torque method, and preload requirement govern.

The tensile-stress-area formula and the SAE J429 grade strengths are published in standard fastener references; the grade is read from the bolt head markings.

Estimate. AHJ and licensed professional govern.

Field names used by the API: nominal_diameter_in, threads_per_inch, grade, at_in2, proof_load_lb, tensile_load_lb, rec_clamp_lb

• Stress area At = 0.7854 x (D - 0.9743/n)^2 at the thread root, ~15% under the nominal shank areaASME B1.1 / SAE J429
• Grade sets strength the grade read from the head markings sets proof, yield, and tensile strengthSAE J429
• Recommended clamp about 75% of proof leaves margin for torque scatter and service loadsfastener practice