The sliding door in my garage has a few holes from a different handle and they really needed to be repaired. The holes are slightly over 10mm in diameter so I made the barrels 10mm to give me a snug fit and to keep the plug nicely aligned in the hole. The caps come in two diameters (15mm and 20mm) in case like me, you need to cover flared holes. Depending on the state of your hole and the potential to foul on the door frame, you may need to use a 15mm cap on one side and a 20mm cap on the other. Mix and match as you please.
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The barrel nut needs to be at least 30% and I did the screw at 100%
One hole done, here I am taking care of the second hole.