Review on 🔧 Allstar Performance ALL50855 Bleeder Screw Cap - Set of 10: High-Quality Solution for Effective Brake System Maintenance by Paul Williams

These things are certainly not cheap, but they are almost impossible to find in stores. They fit over the bleed screw and keep dirt and dust out and hopefully prevent it from binding and freezing up. In most cars they are already installed, but over time they fall off, crack or simply disappear during maintenance. I've heard of some guys who put a drop of silicone paste on the bottom of the vent hole and then put it on top to prevent rust. If you've ever dealt with a frozen bleeder valve, you know what a pain it is, and for the average person, that means buying a new $60 caliper. This makes sense accordingly.