Yeah, mine is like your second picture for the SM420. It has a ring of ridges around the outside for grip but they're about worn smooth at the top from years of use I guess. I looked but no part #.
Jeff

"Do not walk behind me, for I may not lead. Do not walk ahead of me, for I may not follow. Do not walk beside me either. Just leave me alone, you're starting to freak me out."

1957 GMC 150