if you are talking 3inches well one inch is 25.4mm x 3 =76.2mm metric so 76.2x2 =152.4mm thats six inches thats the best way to work it out its is no way 3mm amigo your maths don't make sence
if you are talking 3inches well one inch is 25.4mm x 3 =76.2mm metric so 76.2x2 =152.4mm thats six inches thats the best way to work it out its is no way 3mm amigo your maths don't make sence