This buckle of the strap is diffcult to install if you are not professional because it used clip pins instead of spring bars like other brand watches'. Buyer can search your local video on website about how to install buckles for Longines. If you buy strap without buckle, you might need a local jeweller to intsall, so i suggest you buy with clasp, that would be easy for people who might not know how to install buckle.Sometimes you need a jeweller to help you install. for 13mm Width: 105+70mm length.with lg on band and buckle. Buckle size 12mm. for 14mm Width: 105+70mm length.with lg on band and buckle. Buckle size 14mm. for 15mm Width: 110+70mm length.with lg on band and buckle. Buckle size 14mm. for 18,19,20,21mm Width:115+75mm Length.with lg on band and buckle, Buckle size 18mm. for 22mm Width: 120+75mm Length. with lg on band and buckle, Buckle size 20m.