My Umarex Fusion 2 first needed o-rings for the pellet probe / bolt. They sent me a whole new bolt which I had no clue how to put in. I removed the o-rings and swapped them to my bolt. My determination is 4.7 OD, 2.5 ID and 1.0 thick (.185 / .0984 / .040). Now the INNER o-ring on the CO2 tube...