ZCI Nylon Bearing Piston Head

I didn't have a problem using this with a #14 o-ring as the other reviewer did...could be a different batch or something. Great light piston head, does the trick for the price—very cost effective. The ONLY issue I had was in my attempt to make sure it didn't come loose, I tightened it TOO much on a piston and actually ended up with a spider web crack over the top of the piston before I had even reassembled the gearbox. The ball bearings are nice though, pair this with a ball bearing spring guide and you are good to go with the flow.