My version. It's similar. I wanted the inner surface of the spring to be accessible from all angles while bead blasting, so I used two threaded rods on the outside. Angle iron "tilted" to much while extending a spring so I went to 3/4 inch square tubing.
Parts required:
2 each 3/4 inch square tube, 5 inches long
2 each 3/8-16x6 inch long threaded rod
4 each 3/8-16 hex nuts
4 each 3/8 flat washers, to act more of a bearing surface
Remember, springs are usually heat treated so they will be dark.
Jim