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 makes it easier to put on and take off your fins. This product comes with two types of buckles (16mm and 20mm) making it suitable for fins with different connection sizes. Spring Straps: These scuba fin straps feature springs that automatically tighten without the need for adjustment. They are simple in structure yet lightweight and sturdy. Quick Release Buckle: The quick release buckle design makes it easy to put on and take off your fins swiftly and conveniently. Package Includes: Each package contains a pair of straps. Please note that due to their larger size and weight, these straps may not be suitable for smaller or lighter fins where the size and weight may not be balanced. Specification: Material: TPR PVC Size Chart: S: Spring length 27.2cm//10.71inch for shoe size 36 to 40 R: Spring length 29cm/11.42inch for shoe size 41 to 44 XL: Spring length 30.5cm/12.01inch for shoe size 45 to 47 Buckle A: 2cm/0.79inch : 1.6cm/0.63inch Buckle C: 1.6cm/0.63inch Package Includes: 1 pairDiving Fin Heel Note: Please allow slightly errors 1-2cm differences due to manual measurement.