This is the plastic insert that is part of the Complete Lens Ring Clamp. If you are building your own, you will need to buy a metal clamp and a lens ring plate.
Below are our current models of lens ring mounts, using different metal ring (LR) and lens ring plate (LRP) and plastic insert specific for the lens.
Lens Ring Component Build Chart PDF file: http://www.nodalninja.com/Manuals/Lens_Ring_Component_Build_Chart_v914.pdf
Images may vary from actual product.