Copper would help give more support to the drop ear fitting and tub spout which is probably why they recommend it.
Why can t you use pex for tub spout drop.
Original poster 4 points 3 years ago.
2 reasons i learned.
Copper is the only professional installation material.
Use a drop ear bend support to hold the tubing in a tight bend right.
With a built in diverter you could use a pex drop eared ninety degree female adapter and a nipple but that is more trouble than it is worth.
If you use pex for the tub spout when you turn on the water to the tub water will back up through the shower head due to the reduced inner diameter of the pex it s called stacking.
Also a lot of tub spouts have installation methods that only work with copper stub outs.
The interior diameter of pex is actually a fraction smaller than copper this forces water to come out of the shower at the same time as the tub spout.
A lot of manufacturers are very specific about this and i ve seen it hundreds of times.
You can connect a compression type shutoff valve to the one half inch copper stub out and then connect your fixture.
Why can t you use pex for a tub spout.
In areas that are concealed like under a kitchen sink or vanity cabinet you can eliminate a joint by running pex supply directly to the shutoff valve.