I didn't want to use the plastic coupler that was molded to the nose cone.
Making something close to the original would take a little extra work.
The Enerjet assembly drawing shows a blow-molded plastic adapter with only .10" exposed between the joined tubes.
A JTC-13 black coupler was ordered from Semroc. I used my Odd'l Rockets tube cutter to make a .10" piece of ST-13 to slip over the coupler.
The coupler is only 1 1/2" long. I wanted a longer shoulder into the lower tube. I decided to glue the .10" piece so that a 7/8" shoulder would slide into the lower end. The upper side of the coupler is left with 1/2" for gluing into the upper ST-13 tube.
For some reason, I kept the balsa shoulder I had cut off an old BT-60 nose cone. This would go into the lower end of the coupler and allow for a screw eye attachment.
I set the coupler over the scrap shoulder and drew a pencil line around the inside. The balsa was carved down close to the inside coupler diameter. It was friction fit into place. I left a little overhang of the lower end and sanded flush with a sanding block.
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