OMS Spring Heel Straps for Slipstream-Style Fins can be worn with most fin types. OMS Spring Heels provide divers excellent fit and comfort and make the divers fins easy to don  and doff quickly. Features Automatically adjust to the divers feet Compensates for depth and compression of boot material Unbreakable strap provides an amazing degree of comfort and peace of mind Stainless steel main spring and safety cable wrapped in durable fabric Heal Sizing: Small @ Relaxed = 16 cm Small @ Stretched  = 25 cm Medium @ Relaxed = 18 cm Medium @ Stretched  = 27 cm Large @ Relaxed = 21,5 cm Large @ Stretched= 30,5 cm XLarge @ Relaxed = 24 cm XLarge @ Stretched = 33 cm XXLarge @ Relaxed = 28 cm XXLarge @ Stretched = 35,5 cm