These hardened steel taps correspond to headstock thread sizes to let you make wooden fixtures such as glue and jam chucks, or special face plates.
You simply drill a block of wood (using either a lathe chuck or a drill press), tap it, and then thread it onto the headstock spindle for facing off with a scraper or skew chisel. Work holders made this way run very true because they are turned directly on the lathe.
The 1" tap requires a 7/8" hole, while the 1 1/4" tap requires a 1 1/8" hole. The 33mm tap requires a 1 3/16" hole.
An easy way to make inexpensive custom lathe accessories.