If you are trying to install a screw-on tub spout, it might not tighten up, because the SharkBite adapter will spin. You would need to use a wrench to tighten the SharkBite side, and that would be hard to do inside the spout.
Some spout basics:
Diverter vs tub only
- Diverter spout models have a pull up knob that blocks the water flow, causing it to reverse and come out the shower head.
- Tub only are just simple spouts, filling the tub.
Spout connection types There are three main types of how a spout connects to the pipe
1 Front threaded. The pipe traverses the length of the spout internally, ending in a threaded fitting (usually 1/2" IPS). A front threaded spout usually does not integrate a diverter.
2 Rear threaded. The pipe connection is made at the rear of the spout. These spouts can be either diverters or tub only.
3 Slip on. These spouts will work with just a clean, open copper pipe, as it has a set screw adapter to clamp the pipe.
Soldering to the nipple with the PEX attached is not optimum, but can be managed if you have room to tightly wrap a water saturated cotton rag around the copper and extended over the PEX portion. The water won't allow the PEX connection to go above 212 until it dries out. You will need several inches of bare copper pipe on the end to solder to. (Just TRY to a solder a pipe with any water in it.) Practice your soldering ahead of time and you will become confident of solid, leak free joints.
This thread has some good advice on soldering
This page describes tub spouts.
Answer from HerrBag on Stack ExchangeTub Spout, Plumber used Sharkbite and Pex
plumbing - Can I use SharkBite connectors on a copper stub out? - Home Improvement Stack Exchange
Can I use sharkbites to replace a shower valve? - DoItYourself.com Community Forums
plumbing - How to avoid spinng sharkbite on moen spout? - Home Improvement Stack Exchange
What are the shipping options for SharkBite Tub & Shower Valves?
What's the best-rated product in SharkBite Tub & Shower Valves?
What's the cheapest option available within SharkBite Tub & Shower Valves?
Videos
Installing the tub spout appears impossible as the sharkbite just starts to spin inside the wall when crank I it down. What can I do?
If you are trying to install a screw-on tub spout, it might not tighten up, because the SharkBite adapter will spin. You would need to use a wrench to tighten the SharkBite side, and that would be hard to do inside the spout.
Some spout basics:
Diverter vs tub only
- Diverter spout models have a pull up knob that blocks the water flow, causing it to reverse and come out the shower head.
- Tub only are just simple spouts, filling the tub.
Spout connection types There are three main types of how a spout connects to the pipe
1 Front threaded. The pipe traverses the length of the spout internally, ending in a threaded fitting (usually 1/2" IPS). A front threaded spout usually does not integrate a diverter.
2 Rear threaded. The pipe connection is made at the rear of the spout. These spouts can be either diverters or tub only.
3 Slip on. These spouts will work with just a clean, open copper pipe, as it has a set screw adapter to clamp the pipe.
Soldering to the nipple with the PEX attached is not optimum, but can be managed if you have room to tightly wrap a water saturated cotton rag around the copper and extended over the PEX portion. The water won't allow the PEX connection to go above 212 until it dries out. You will need several inches of bare copper pipe on the end to solder to. (Just TRY to a solder a pipe with any water in it.) Practice your soldering ahead of time and you will become confident of solid, leak free joints.
This thread has some good advice on soldering
This page describes tub spouts.
Here's a bathtub spout install with sharkbite. Run a length of 1/2 copper pipe as needed from bottom outlet of mixer (use 1/2” female sharkbite adapter) to about 4 inches above rim of bathtub. At bottom end of cooper pipe install a 1/2” sharkbite shower adapter upside down. Get a 1/2” steel pipe threaded at both ends from any hardware store. Screw one end into the spout until tight then screw the other end protruding from spout into the shower adapter. Use “tuff” at both ends to avoid leaks. I use a 6” steel pipe. That’s it. Works fine. (I’m not a plumber >>> DIY)