Sunnex valve grinder model 645

I just bought an old Sunnex valve grinder from a friend of mine who is a wheeler dealer. I figured I might use it on my Plymouth. What is this part that I found laying in the tray? I have not ground valves since high school

 

lol I meant to say Souix. It’s a Souix 645

 

That's the wrench you use to loosen the set screw to adjust the position of the chuck stop that locates the stem end of the valve in the chuck. That rod with the flat that protrudes out the left end of the chuck spindle has an inverted cone in it for the valve tip to seat into. The knurled collar on the left end of the chuck spindle is where that set screw is.