Reducing Bushings are to connect a FPT thread to a reduced size of a MPT fitting.
These fittings are slightly different than couplings..
Bushings, unlike couplings, tend to have threaded ends, although some
models do have slip ends. This allows for a tight seal without the need
to use an adhesive product. This works well in situations where the
pipes may need to be removed or replaced regularly and flow or pipe size