You MUST use a metric ruler to get the correct measurements for any and all fold over clasps

1 mm = just over 1/32 inch
2 mm = just over 1/16 inch
3 mm = almost 1/8 inch
4 mm = 5/32 inch (= a bit over 1/8 inch)
5 mm = just over 3/16 inch
6 mm = almost 1/4 inch