I changed my oil on my raptor on Saturday for the first time ( I just bought it last week). It's an 07 700 & I believe it was a 21mm. Hope I'm giving you the right size
EDIT: I'm not sure if I understood your question correctly. If you are talking about the diameter of the hole and the type of thread that the drain plug underneath the engine uses, then I have absolutely no idea . However, if you are wondering the size of the head of the drain plug bolt it should be 21mm.