Our bolts are manufactured to comply to ANSI Standard B18.2.1 / A2 304 and A4 316. Supacheap Bolts currently stock 1/4", 5/16", 3/8", 1/2" and 5/8" diameter bolts up to 5" long in certain diameters in Fresh Water Grade 304 and Marine Grade 316. Please note : Our Image is of a generic standard bolt and nut and thread lengths vary slightly per size so check with us before ordering if this dimension is of importance. Typically, thread lengths for our hex bolts will be to the recognised Australian or International standard. All bolt lengths are measured from under the head.