Can A325 and A490 structural bolts be supplied with fine thread?

No. The specification calls out that those bolts must be Unified National Coarse thread and have class 2A tolerances.

The F3125/F3125M specification reads:

4.2 Threads:

4.2.1 Uncoated bolt threads shall be as specified in Table 1.

4.2.2 Coated bolts shall have threads meeting Table 1 requirements before coating.


Thread Fit, ASME 120 ksi Min Tensile Strength


150 ksi Min Tensile Strength


Type 1 Type 3 Type 1 Type 3
B1.1 UNC 2A B1.1 UNC 2A B1.1 UNC 2A B1.1 UNC 2A
Written ,


    I have a planetary axle shaft with a castle nut for preload for a tapered roller bearing. I’m replacing bearings, seals & race. I the threads seem to be NF, I measured 8 full circumference threads on a 5/8″ thick castle nut.
    The axle shaft has one full circumference of thread missing. The nut will engage the missing thread when torqued. Mfg torque spec is 400-450 ft-lbs for bearing load. The axle shaft is 2.250″ in diameter.
    I feel I have enough threads with 7 threads to hold this torque load as it is pretty low for this size hardware & it his secured with a castle nut style of retention.
    Just asking your opinion?

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