This kit is just what I needed to fix an old plug that was starting to leak. I stuck a lot of tires myself, so I just took the thing out of the box and drove into town. It was very difficult to pull the gun's trigger, and the three plugs could not fully capture the tire even when the tool was fully seated. THEN I read the instructions. The plug goes into the gun so the little mushroom is like an umbrella turned inside out, and if it becomes difficult to pull the trigger, release the pressure on the gun like a caulking gun and then try again. I thought that part was stupid, but it worked! The cork will hold 100% air at 55psi after a few days.