What Size Hole Needs to be Drilled to Install 2-1/2 inch Optronics Clearance Light MC57RB

I am adding some lights to the back of a 2-ton truck body. I want to use the 2 1/2inch recessed lights for this and I was wondering what size hole they require for mounting. I purchased 4inch lights but I dont have enough room for the hole on the back of the body. Any help on this would be appreciated.

asked by: Willi S