There have been 3rd party manufactures and pre-shopsmith owners who could have made just about any thing.
I think the groove and notched washer are something these need to have depending on what is mounted, and while perhaps they did not pay much attention to those safety factors in the old days it is an improvement that one should look for today.
I would like to see a picture of it if you can. I'm guessing it would look pretty much like the one I have minus the groove but if it were an older design or 3rd party then maybe not.
Ed
garys wrote:While looking through my Shopsmith drawer I found an extra 5/8" arbor that I'm not sure exactly what it is.
I have one of the Shopsmith 5/8" molder/dado arbors listed here and I know what that one is.
http://www.shopsmith.com/ownersite/cata ... oarbor.htm
The extra one is very similar, but a bit shorter, 1/8-1/4" less on the bolt end. It doesn't have the 3/4" thick washer that the molder/dado arbor has, and it lacks the groove in the bolt for the locking tongue washer. It has been with my Shopsmith for decades, but I don't remember what it is for. I have used it with my wobble dado, but it isn't quite long enough for my multi-blade dado when set to maximum width. Is it maybe just an earlier version of the molder/dado arbor?