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