Review on HK Army Thread Protector Black by Jeffery Pricinoc

Does what it says on the tin. Screw it in and you don't have to worry about stripped threads or dust and dirt getting into the pin valve. It also holds up well. I've never tried using spare o-rings on top as they will likely dry out and crack anyway. Tip: Choose a color that contrasts with the inside of your gear bag. My bag is black so I use a silver threadguard. Makes it easier to find what you need at the end of the day. It also helps to have a pocket to keep the protector in at all times when you take it out of the tank.