We really try to make these product descriptions entertaining and enjoyable as much as we can. But sometimes, we just feel like being blunt. So here you go: This is a shim. Said shim will allow you to run any of our 1″ Ring Light Mounts with some lights that are smaller in diameter than 1″. This shim is one piece with a 1/16″ slit and made of black acetal (also known as Polyoxymethylene or Delrin), a durable homopolymer that we enjoy machining from time to time. Since the outside is 1″ in diameter this shim will also work with other light mounts on the market, if you so need, but is toleranced and sized specifically for our light mounts to give a near seamless appearance. Currently we have 2 sizes available: One for lights with a 0.875″ outer diameter of which the Fenix PD35 is a shining example, and the other for 0.825″ outer diameter lights such as the fine E-Series lights from Surefire. Make sure you choose the correct size from the drop down menu when placing your order.