It is made for IWC IW377717 watches which has 21mm lugs. 22MM SOFT RUBBER DIVER WATCH STRAP FOR FIT IWC PILOT PORTUGUESE TOP GUN BLACK. 17MM 18MM 19MM 20MM 21MM 22MM 23MM 24MM 26MM. Strap is 21mm at lugs and 18mm at the buckle and you can interchange with the buckle.
eBay