20 CURVED Whistle Buckles 1/2" (13mm), Black & Orange, Great for Paracord Bracelets. Emergency. Whistle Buckle Side Release Buckle Contoured For 1/2" (13mm) webbing or straps. 1 13/16" (46mm) long x 13/16" (21mm) wide. 1 1/16" (27mm) wide counting whistle tip. Each opening is 1/2" x 3/16" (13mm x 4.5mm)