Taylor, 18 gage is about .047" thick.
Dave, I run the center mandrel through once. I curve the sheet metal by hand until it fits into the female/outer section. I drive the mandrel in from what will be the front of the nose cap. Once it is flush with the top, both inner and outer pieces are the same length, I pean over the front end. Lube is the key. The 2 set screws were going to be used to take up the space on the backside of the fixture where the nose cap did not go all the way around. I ended up just using a scrap piece of sheet metal to shim up the area.
DMR