while trying to find the rubber strap for IWC 3527. The issue is that rubber straps from that era have metal inserts which must match the grooves of the watch case. In my case the rubber strap from 3538 didn't fit 3527. IWC concierge wasn't helpful at all, neither was IWC boutique in NYC. IWC AD in las Vegas helped me to find the right strap. One thing to keep in mind is that if you buy a strap directly from IWC they are returnable if unworn and tags are intact.