Scope Adjustment Ring - 44mm or 1 3/4 inches

A pretty basic model, but I figured I'd publish it just in case anyone else got use out of it. 

Once printed, you need to pry the gap open to insert an M3 threaded heat set insert. 

My biggest tip is when doing this, use the “backwards” technique. Insert a somewhat long M3 screw into the opposite side of where the solder iron needs to be (i.e on the outside of the ring) and thread it into the M3 heat set insert, which will both let you pull that arm of the circle open, as well as keep the heat set insert perfectly aligned. Then apply the hot soldering iron, while pulling the heat set insert into the hole with the long M3 screw. It's a bit tricky, but it's about the only way to accomplish this installation of a heat set insert into such a small gap.

No supports needed, but print at 100% infill, as it's a small part, and you're going to be melting a heat set insert into it, which really requires a solid chuck of plastic.