Round, white, hard UHMW slide pucks from those cats at Landyachtz.
These pucks are long lasting (unless your friends steal them, and should be top of your list for puck replacements.
**Set of two.
Rough velcro is attached to the pucks (for a standard slide glove make). We note this for our friends making their own gloves - make sure the soft velcro is on the glove.