An Optional velcro strap in black or gray was made available – these straps connected to the initial male connection of the bracelet. Luckily, The material strap with the IW3715-36 as well as alternate rubber strap from your IW3548 match the Aquatimer! Christie’s This was mostly a ref. 6538 — https://www.watchesworld.com/frozen-in-time-luxury-watches-for-winter/