It isn't so much the thickness of the strap, but the thickness of the loop of leather around the springbar. The distance from the strap holes to the body of the watch is relatively short on tungsten watches. I have a 5mm thick strap I had custom made on my M27, but the loop had to be made thin enough to work. I have some nice straps for my Panerai that rub on the case. The watch strap maker I used is familiar with the tungsten case so she knows about the reduced space around the springbar.