18500/18650 square tube holder

This thing is made to hold an 18xxx-type Li-ion battery inside a 1-inch square aluminum tube. With 1/16-inch walls, that makes the inside length 7/8 inches. This is for a bicycle light project using 10V, 10W LEDs mounted directly to the outside of the tube, with batteries and current regulator inside. I'm still looking for a prebuilt regulator. :-) I'll design it if I have to, but I have seen inexpensive switching regs for cheap.

The part is only 20mm tall; stretch it Z-wise to the