Yai - a no 1. is 1/8" or 3.18mm;
no 2. is �" or 6.35 mm; no 3. is 3/8" or 9.5mm and a no 4. is �" or 12.7 mm. The range also goes above 5, 7, etc[up to a no 15 [I think] and down to a 000] Go to a hair salon supplies shop - Sallys Salon Suppliesclick here for store locator is a nationwide chain. You can buy the various guards in there [in the US they're called combs] they also usually have the length written on the back, near what grade it is.