Glad you got the plugs, Rob. When you drive the plastic ball that seals the fill hole in an OEM cart into the reservoir area this plug is designed to fit perfectly. I guess that the constriction toward the end ot the plug (rather phallic) is supposed to engage the plastic seat that the ball was on. One of my OEM carts wouldn't hold the plug. It kept creeping up. I checked all my OEM refilled carts with a 5/32 drill bit and found that all of them except for the errant cart had a clear 5/32 fill hole. When I hand reamed it out with the drill the plug then worked fine.