Originally Posted by 3alarmer

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...If it's a square taper spindle, the threading is pretty standard, just the heads of the bolts come in different sizes.

Originally Posted by HillRider

The threading is usually M8x1.0mm. This is a finer thread than the more commonly available M8x1.25mm but bike shops or better hardware and industrial supply shops will have the proper bolts. As noted, the head configuration can vary among bb and crank makers.