Great addition to any polisher. Needed for on my Swirl Killer and SK mini. Instructions on the Adam's site are a little confusing because it says to put two lock washers on , but it only comes with one. But you don't need it. For the SK polishers, use one lock washer and both spacers and the big bolt. Works great!! Definitely needed and helpful especially if you don't have the best light in the garage.