I use something similar to the PSI sander/jig, but I was not satisfied with how tight my miter gauge (with their jig clamped in it) fit in the miter slot on my Craftsman belt/disc sander, so I built my own using their concept. I used "D" drill rod (0.246 inches). I already have pretty much a full set of sleeves for it along with a few that I made myself by turning down a blank on a 7mm tube, so I included a storage spot for them.
If I had it all to do over again, instead of using a fixed "D" drill rod, I would have made the jig with a "V" notch and clamp arrangement to accommodate various sizes of transfer punches instead of the drill rod. By choosing an appropriately sized transfer punch for each tube I would not have needed the sleeves. I am sure that my jig version 3.0 will be designed that way. After all, I will still be able to clamp a piece of "D" drill rod in the "V" notch it and use the sleeves instead of transfer punches if I should want to.
Anyhow, here are a couple of pictures of my sander and squaring jig 2.0. For the most part the whole thing was made by gluing pieces of 1/2-inch Baltic birch plywood together and the sleeves are stored on 1/4-inch shelf pins.
Dave