whats this bit called?

[an0nymous]

I have an old rusty pexto 544 thats fallen into my hands. On the bench mount the piece outlined in red is missing. Come to think of it, I have a few c clamps missing the same thing.
I imagine they are just press fit over the ball, right?
What's that called? is there a good place to buy replacements?

 

[p_mori7]

Swivel Head.

 

[an0nymous]

...and that lead me to Replacement Swivel Pads for C-Clamps on mcMaster-Carr.
Just what I was looking for, thanks!