These freeze down hacks are for arena clubs, or wherever you need to add hacks temporarily. To freeze them in, heat each hack in a 5-gallon bucket of hot water, set on the ice, and stand on them for a minute or so. Allow to freeze for 5 minutes and you are good to go. To remove, gently pry under the hack with a pick or similar lever.
Sold as single units - purchase two for each sheet of ice. Hack rubbers are purchased separately.