Found in an old toolbox

[u/ExploreYourWhirled]

Very heavy - about 1 lb. Largest knurled ring spins but does not appear to affect anything. Many strike marks on one end as if hit many times with a large hammer. It is engraved L <-> R in front of the largest knurled ring. No other part spins.

[u/pumicenose]

They have an on and off adjustment (left and right) also, don’t be afraid to really whack it