> (modern ones have loose combs that are held in a steel head)
Terminology in the US is totally screwy, Millstone dressers hammer, but also called a Bush hammer (it is , but only the small size is used for millstones, stone workers have larger sized ones also), also a Millers hammer, or a Masons large breaking hammer. also a furrowing hammer, in spite of the fact it isn't used to make the furrows (a different hammer is, originally a Millstone pick, even tho it really a hammer)
Knight's also shows a Bush type Furrowing hammer with a single leaf in one side, so I guess it could make a grove also
Oddly, the the top millstone in a horizontal mill was also called a millstone hammer....