While it is fairly obviouse that a cutoff hardy goes with the hardy hole, there are many other tools that may be used in the anvil by adding a square shank that fits your hardy hole.

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The following list provides just a few resources to help you find supplies and equipment for blacksmithing.
http://www.piehtoolco.com/
http://www.centaurforge.com/
https://www.blacksmithsdepot.com/
http://www.blacksmithbolt.com/
https://www.oldworldanvils.com/
http://www.nimbaanvils.com/
http://fontaninianvilandtool.com/
https://www.abana.org/
http://www.mcmaster.com
https://kensironstore.com/

Blacksmithing and related activities can be hazardous. These videos are not a substitute for competent professional instruction. Your safety is your sole responsibility. Always use appropriate safety equipment including eye and ear protection when working in the shop. Follow manufactures safety guidelines for the use of all equipment. In the event something shown in one of these videos seems unsafe, it is up to you to make the appropriate changes to protect yourself.