Bottom bracket unit in a frame made for the old-style "Ashtabula" one-piece cranks.
The 24 TPI threading fits most one-piece cranks.
(If your bike is a Schwinn or Mongoose, and you are using the original crank, you probably need the 28 tpi version.)
If you are replacing the original crank even on a Schwinn or Mongoose, this 24 tpi set is the way to go. The old 28 tpi threading is an endangered species, but the frame will accept either type with no problem.