As Breeze3at stated, they should be the same size.Yours may have been stripped then re-threaded. I find it much easier & cleaner to do timing with this method. Drain primary fluid.Open the inspection cover for the primary chain. Rotate the engine to get the timing mark in the window, then clean off the the Rotor & inner primary with carb. cleaner real good at the 3 o,clock position.Take a colored Sharpie pen & make a line from the rotor to the Inner primary.Put you plug back in the the timing hole. You can the use those lines to do your timing with a light. No oil blowing out the the timing hole to get all over you or your timing light.Ck. your primary chain tension,refill with fluid, good to go. I usually have a friend help so I don't have to go from 1 side to the other as I move the timing plate.