Original Craftsman Multi Speed Attachment or "MSA". Usually the smallest sheave on these pulleys is extremely worn but this one's in very good shape. The pulley has new bearings and includes the collar and both garter springs, so it'll fit either the King-Seeley/Craftsman Model 100 or 150 using the collar or the Model 80 without the collar. 

I also often see these on the Delta 14" (DP-220) and many other machines with a 2-3/4" column.