Many metric sized fasteners do not have equivalent imperial / standard sizes. Anything with machine screw threads (parts that must fit an equivalent nut or hole) can't be equated to standard US sized fasteners. Nuts can also not be crossed with standard sizes, as there is no equivalency in thread counts.

However, other part styles (self-tapping screws, self-drilling screws, rivets and washers, for example) which don't require an exact match in hole / thread size, can use equivalent standard sizes.

We've created a quick and easy inch to millimeter calculator to help find standard part sizes that may work when metric sizes aren't available.

For example if you have a screw and only know that the description is M6 x 25 millimeters, you can find that the M6 diameter equals .23622, and the length of 25mm equals .98425. Once you have that information, you can see that a 1/4" x 1" screw would be a very close size match.