An Optional velcro strap in black or grey was made available – these straps attached to the main male hyperlink in the bracelet. Fortunately, The material strap with the IW3715-36 as well as the alternate rubber strap within the IW3548 fit the Aquatimer! Christie’s This was mainly a ref. 6538 https://www.watchesworld.com/frozen-in-time-luxury-watches-for-winter/