Review on 6PCS Presta to Schrader Valve Adaptors for Bike, Convert Presta Valve, Inflate Tire with Standard Pump or Air Compressor, Includes 12PCS Tire Valve Caps by Alex Webster

In my experience they are a bit small. This is how the thread works and is screwed onto the Presta valve. but they leaked when I connected them to the pump. If you have a big compressor, you can pump air up fast enough, so it doesn't matter, but with a hand pump or some other slower type, I was losing air faster than I could pump air into the tire. So I compared them to other adapters that work well. The ones that work well are slightly larger in diameter and therefore seal well. It's only a fraction of a centimeter that matters. So they are almost useless.