Today I installed a Delta Monitor 13/14 valve body for my bathtub/shower. It has four threaded 1/2" ports.

I screwed on female compression fit connectors. The hot and cold inlets leak. The hot is just a slow drip, the cold barely at all but it does drip. Both from the threads. I used a less expensive copper fitting on the hot inlet, and a more expensive brass fitting on the cold inlet. Luckily, I had the foresight to install shut-off valves. Now we can shower then turn off the water supply.

What to do about the drip? I tried it with and without teflon tape. I cranked the fittings on as tightly as I dared so as not to wreck it. My next solution will be to sweat (that's a new word I learned today) the threads.

How much Teflon tape did you put on the threads? Do you have any pipe dope(paste thread sealant)?

I only put one wrap of teflon. I had done more for other projects but wanted to make sure the fittings got on as far as possible without the tape getting in the way.

No dope, but that was another thought.

You need 3 or 4 wraps of thread tape, wrap it clockwise on the threads, a few drops of pipe dope makes it even more leak proof.
I always sweat pipe or fittings into those valves.

there is no excuse for leaking threads if everything is new.. don't want to sound harsh but if the male threads had teflon tape wrapper clockwise with some pipe dope spread ontop and they were tighten properly, they will not leak.
why not do as north carolins suggested? 1/2 inch copper fits perfectly inside those ends.