I purchased a mill a year or so ago without much knowledge of actually using one but with high hopes. I've learned a lot and still have a lot to go. With the tooling the gentleman supplied with it came this arbor and all of these cutters, which I've not used. All of them are marked USA and for the most part seem sharp enough but I don't really know anything else about them. If any of you have knowledge to share I'd be really grateful. I will probably use a thin one in some 6061 Aluminum in the near future so I wanted to see if any of you had some specific advice in regards to what they actually are and any specific uses they are intended for. I'll be using a thin one to make a slit through a side of a collar after I drill and tap a hole for a screw to go in and tighten down on a separate piece, if that makes sense. The larger diameter ones fit this arbor on the right, which I can only assume he had made for them but the cutters are keyed and this arbor does not have a key way. Also, the "neck" that they slide onto is too long and would require washers in order to get a tight fit. -John