This is the Suunto 24mm Dive 1 Silicone Extension Strap For D5 Scuba Diving Computer Features: Robust strap designed for diving Strap width 24mm Strap weight 19g Fits wrist sizes up to 330mm Compatible with Suunto D5, Suunto Spartan Sport, Spartan Sport Wrist HR, Spartan Sport Wrist HR Baro, Suunto 7 and Suunto 9 The silicone extension strap enables you to wear your Suunto D5 over your wetsuit or dry suit. In addition to Suunto D5, the extension strap is compatible with selected sports watches for use over layered clothing.