I recently purchased an aftermarket strap that came with a buckle. Today I was at the local boutique and decided to spring for a genuine buckle. I'm not thrilled with what the factory charges for genuine parts, but here is what I noticed.

The IWC buckle is branded, and the pin is stamped instead of bent. And there is a recess for the pin.
The IWC buckle has a far better finish and is marked as to origin.
