Works very well, the threads are very precise when attached to the valve stem and it really does feel like it does it doesn't let dirt/moisture in and it's entirely possible to even stop or reduce it to minimize air leakage from the old, running valve. It has a very good rubber pad/seal around the top that noticeably snaps when fully screwed in. One note though: the product I received was actually a medium shade of gray, not black like the product image. But for a pack of 100 quality caps, the color is almost trivial if it's a somewhat neutral color. Certainly better than paying $4-$10 for a 4/8 pack. Also suitable for standard valve stems as well as stems from tire pressure monitoring systems (TPMS). Mine are now on standard shanks.