As you turn the two pieces of 1/4" MDF, the acrylic washers / bolts move in and out from the center of the device.
To see it work, click here: https://www.youtube.com/watch?v=y1Si49jzygg
You could also use this to make an iris if you wanted to do so.
Step 1: Laser Cut Two Pieces of 1/4" MDF
Step 2: Cut Washers Out of 1/4" Acrylic
I bought eight (8) 1 1/4" bolts and nuts from Home Depot.
Step 3: Bolt the Two MDF Rings Together
You need to have a nut that will lock at a specific point and not prevent the two disks from rotating.
I made it at Tech Shop.