... metric unit(mm)1/4" x 1/4"6.4mm x 6.4mm22,23,243/8" x 3/8"10.6mm x 10.6mm19,20,21 ... 7mm x 12.7mm16,17,18,19,20,21,22,235/8" x 5/8"16mm x 16mm18,19,20,21,3/4" x 3/4 ... "19.1mm x 19.1mm16,17,18,19 ... ,20,211" x 1/2"25 ... .4mm x 12.7mm16,17 ...