Just slide them over top of your 1/16", 1/8", 3/16" or 1/4" part pin them down through the laser cut pinholes and PC Rib Jig will hold your part straight up and down so you can glue your fingers to it. (You know your going to).
They come in a set of 12 jigs. 3 of each size. Plus you get one of the multi sized jigs along with it. So, really, I guess its a set of 13. Math is not my strong suit.
Since work space is hard to come by, we made a really slick holder to put them on when they are not in use. That stops you from stacking them in the corner, knocking them over and stepping on them like I would.
They are cut from 1/8 MDF and over all are 3.75" tall and the rib slots are 2.75" deep. At 1.5" wide at the base, they should easily fit between your parts, unless your parts are smaller than most peoples'.