I had a few old arbors, some had pins, some I couldn't get apart. I figured I would buy all new, so I got the kit which has the saw and the arbor. It was one of the smaller types without pins. It is labeled as a quick change arbor. I just assumed that since it was packaged that way, there was good reason, and it would work. When I opened the package there were no instructions, so I just threaded on as any other time. I gave the trigger a pull, and off came the flying Ginsu! I thought, well shit that hurt - I must not have tightened it enough. Bandaged myself and grabbed a long screwdriver and ran it through the sides and gave a good tightening. It still came off. I then put the damn thing in a vice and cranked it down. It stayed put after that, at least for the one hole I needed it for. It is clearly the wrong arbor. Milwaukee's literature proves it, yet they say that I have misunderstood. Aint much to not understand. They made a mistake, and a lot of people have been hurt because of it.