Casio Black Titanium Watch Strap PRW-5100YT-1, PRW-5100YT
Casio Black Titanium Watch Strap (Link Bracelet) for the PRO TREK Watch Models
PRW-5100YT-1
PRW-5100YT
It also fits:
PRW-5100
PRW-5100-1J
PRW-5100-1ER
PRW-5100-1
(to replace the resin straps)