Promaster 39mm Lens Cap

The center locking mechanism clicks into place with real authority—no more caps popping off in my bag. Fits my 39mm lens snugly without any wobble, which is exactly what you want.

I was a bit skeptical about the center-lock mechanism, but it clicks on securely every time and hasn't popped off once in my bag. The precision molding gives it a snug fit that's noticeably better than my old generic cap.

Finally, a cap that actually stays put—the precision molding fits my 39mm lens perfectly. That center locking system gives a satisfying click and I don't have to worry about it popping off in my bag.