Made this to figure out the measurements for a pen mandrel I wanted to machine. I use it for turning rings. I printed the bushings in tpi or nylon and everything else I machined from metal. To hold the end of the rod you can use a tail stock chuck if you have one but it would be better to buy a $20 live tailstock pen mandrel with bearings that fits the Morse Taper for your lathes tailstock.

The rod is 6.3mm in diameter, 10" long and goes into the base about 2" I tapped a setscrew for #8-32 x 1/4" to hold the rod into the base

You need 4 spacers and 2 bushings for each size: Small 4-7 Med 8-12 Lar 13-14