The plastic buckle set comes in 2 parts, the buckle itself (the thing you clip open and close) and a slip lock (the thing you run the strap through).
These buckles are designed to fit with a compression strap of width of 3cm.
*We sell the strap of this width
$0.50 per set if you buy anything else on nalno.com. One set of buckle and slip lock comes free with purchase of strap