The new lightsaber that Luke creates in Return of the Jedi was completely custom made. The main body was spun out of aluminum on a lathe and is probably hollow on the inside to reduce the weight. The bottom piece was made separately and added on. In the middle of the bottom piece is a section with raised squares, this would be machined as one part (the seam can be seen in the photo above) and a cap piece would then be added on as the very bottom. The raised square in line with the control box has a triangular metal ring to hang the lightsaber on the belt hook.
On the side of the lightsaber is a control box constructed of thin metal. It was made with a slide open cover to show interior detail, presumably this is for the scene cut from the final version of the film where Luke constructs his new lightsaber at Obi-Wan Kenobi's house. The electronics may also run the red and green arrow shaped LEDs on the side of the box.
Close-up of the control box with the interior electronics.
There was an additional resin copy made of this version of the prop. The second photo at top is the resin copy painted to look like the aluminum original. It's nearly identical but there are a few minor differences:
Copper paint - Resin copy has copper paint on the lowest part of the emitter head before the thin neck.
Activation plate - Resin copy has thinner copper lines.
Tri-Ring - Original has a darker metal ring that has rusted, the copy's ring remains silver and is nickel plated.
Click here for more images of the original.