How to put an order?1, Choose the outer diameter and length, akin to "coupling GFZ": if I wish to purchase outer diameter 30mm and size 50mm, then I want GFZ-30X50 or GFZ-30X50-X*X. ( X means within diameter.)2, Pls write the inside diameter length at the order page.3, If you can't find the outer diameter and size size, pls want different size or contact the seller. Normal all size chart we can make for you.Hot items link