I think it is, because it's what fixes the auto gear to the main gear, and the main gear assembly pic shows both the Jesus bolt and the large alloy washer. But it's so cheap that it's worth getting one or two as spares, since it can be marred if your one-way bearing jams.
Very good quality here. The tolerances are just right on this one HobbyKing. They dont wobble around on my gears and are a nice tight fit. Exactly what you want and a top price to go along with it. HK plus1 here.
I've been thru five of these on my HK 450 Pro. If I use governor mode on the ESC, the mainshaft cover wears out and the one way bearing jams after as few as three flights. I think the metal is too soft. It looks like its been eaten away. There seems to be a bit of variation in the length of the parts I have, which means you have to re-shim the mainshaft when you change the cover.
I've yet to try an Align part to see if they're any better, so for now, I don't use governor mode. After around thirty flights, there is noticeable wear in the cover, so i regard it as one of the parts you have to replace on a regular basis, like the plastic links.