I have a tub with a spout that uses a bottom-up diverter. It is old, corroded and does not work properly. I bought a replacement delta top-down diverter spout. The problem is the pipe from the wall is too long and if I screw the new spout on I am left with 1-1.5” of exposed pipe. I am unsure how to proceed. Do I cut the pipe? The new spout has an adaptor for a non-threaded pipe but I am not sure I trust that. Or can I buy a shorter or adjustable adaptor (the long piece of plastic inside the spout that attaches to the wall pipe)? Thanks.

Well you have a choice. You can cut the pipe and solder on another male threaded adapter or you can cut the pipe and use the slip fit adapter.
To use the threaded adapter, measure from the shoulder of the existing adapter to the wall. Reduce that measurement by 1.5 inches and cut the pipe there. Solder on a new adapter.
To use the slip fit adapter simply cut off the existing threaded adapter. The slip fit adapter is quite common. There is no water pressure on the spout and all the slip fitting adapter has to do is hold the spout in place.

I agree with Harold you can go either way, but would suggest to go with the slip type, see the attachment for dimensions, good luck.

John

What is the material of the stubout pipe for spout, copper, galvanized, brass or other material?