Delta single handle faucet balls.
 

Some Delta single handle faucet balls (part #: RP212) that are NOT a
genuine Delta replacement part may be defective. The ball stem should
be firmly attached to the ball and should NOT turn, screw out or move.
If the ball stem is screwing out, do NOT use it. It will eventually
cause the cam to break and the faucet will uncontrollably leak.