Odyssey putter regrip | Golf Monthly

That will be a counter weight.

More likely a finishing cap. SuperStroke putter grips can be counterweighted & it simply screws in. In order to finish the putter grip a lightweight cap is screwed on to cover the hole if a counterweight isn't fitted.

On SuperStroke counterweights they put their name & a weight (50g on the pink one); on caps they put their name twice. If they follow the same form for the Odyssey ones then it will be the cap.