I don’t remember them being a slot head .thought they were a bolt head .I do know they as well as newer pins would break the heads off leaving the pin stuck in . It threads in about a quarter inch then is more like a pin ,the one I had trouble with was on a newer truck and it broke leaving one thread and the pin .I was lucky used a pic to turn it out while wiggling the axle to take the pressure off .Maybee someone put a regular screw in with locktite .The tuff ones at the shop I used to work at the guys cut the pin out with a torch and would have to use a new pin and lock .yours would also have the square block that the pin goes through making it difficult to cut with the toarch.
