I needed a size of one of these to hold a piece of banksia pod for a peppermill I’m working on. They work great and add a little extra meat over typical jam chucks. Also, they allow holding the piece without marring the surface from chuck jaws. I start with a piece of poplar scrap, about a half inch thick and about a half inch bigger or so in outside diameter to what I want to hold. In this example, 1-1/2” is what I want to hold. I drill that first hole about 1/4” deep but that can vary with size of your tenon you want to grip. I follow with a 1-1/4” hole thru. Note that I have marked where this piece of wood aligns in my chuck. I do this anytime I’m going to rechuck something to maintain good centering. Mark a location to cut the piece between jaws, this gives room to clamp. Cut a slit and put back on chuck. Note that if you need more grip you could open the slit a little but the more you open it up or have to stretch the collet to get over the tenon increases the likelihood of losing good centering.