I have a small stash that I've purchased from Midway, possibly Brownells, and Savage. I'm no engineer, but under a lighted magnifier, the detent ball surfaces doesn't look identical. I'm assuming different mfgr sources? As I said, the one that works has a logo, and the underside has recessed areas on both sides of the ball cup. The day I started this thread, I had just installed a new one. It wasn't one of the ones with a logo.