For those of you that have a rotary axis with a 3-jaw chuck, I drew these up to screw onto the end of the project blanks to give the chuck something easy to clamp down on. The crossing flute cuts leave a hole in the center which you can use to align the block with a centerline or center mark you've made on the project blank. The slots let some light in. I didn't have the CNC drill the screw holes as depending on which screws I have handy the hole may need to be a different size, but the countersinks done with a 90 degree v-bit make it easy to drill if you have a drill press. These I cut from 3/4" baltic birch plywood. Feel free to use as is or modify for your own purposes. 1/8" end mill for the flute cuts, 1/2" 90 degree v-bit for the countersinks, and I cut mine out with a 3/16" spiral end mill.