... diameter(BWG) In inch In metric unit(mm)1/4’’*1/4’’6.4mm*6.4mm22,23,243/8’’*3/8’’10.6mm*10.6mm19 ... ,20,21,221/2’’*1/2’’12.7mm*12.7mm16 ... ,17,18,19,20,21,22,235/8’’*5/8’’16mm*16mm18,19 ... ,20,21,3/4’’*3/4’’19.1mm*19.1mm16,17,18,19,20,211’’*1 ...