A double-square screw head is commonly applied on industrial-amount styles as well as haulmark trailers. You will discover non-typical screws are around, Nonetheless they’re commonly labeled for a specific use (for example “eyeglass screws”) as an alternative to discovered by dimension. The subsequent are among the commonest conventional screw dimensions: https://dominickklkjf.kylieblog.com/29848044/lead-screw-thread-for-dummies