That circular thing on the right is the “Plastic Clutch” on the Heathkit HW-101. Mine dried out and shattered when I pushed the “Zero Set” button on the from ot the HW-101. I heard it crack. I cut out a piece of plastic of the right size. That replacement clutch has been in there for about 30 years now.
I know of one other guy who has replaced the clutch on a HW-101 (Will, N5OLA). Let us know if you have done this too. Put a comment down below.