【Material】: The Adjustable Anti-Loose Quick Release Buckle Universal Fin Frog Shoe Heel Strap is made of TPR and PVC material, which is environmentally friendly, skin friendly, and resistant to aging. It remains flexible even in low temperatures. 【Convenient Design】: The quick release buckle design allows for easy donning and doffing of fins. This product includes two types of buckles (16mm and 20mm), making it compatible with fins that have different connection sizes. 【Spring Straps】: These scuba fin straps feature springs that automatically tighten without adjustment. They are simple in structure, lightweight, and durable. 【Quick Release Buckle】: The quick release buckle enables fast and convenient attachment and removal of fins. 【Package Includes】: Each package contains one pair of diving fin heel straps. Please note that due to their size and weight, these straps may not be suitable for smaller or lighter fins where balance could be affected. Specification: Material: TPR, PVC Size Chart: S: Spring length 27.2cm / 10.71 inches – fits shoe sizes 36 to 40 R: Spring length 29cm / 11.42 inches – fits shoe sizes 41 to 44 XL: Spring length 30.5cm / 12.01 inches – fits shoe sizes 45 to 47 Buckle A: 2cm / 0.79 inches x 1.6cm / 0.63 inches Buckle C: 1.6cm / 0.63 inches Package Includes: 1 pair of diving fin heel straps Note: Please allow slight measurement variations of 1–2cm due to manual measuring.