If you have the right contractor, he should be explaining it to you. You obviously don’t have the right contractor. Better regroup. There’s probably a lot more he doesn’t know. Like how to waterproof the wet areas properly.

I also find it extremely odd that you would have to explain a very standard shower configuration to your contractor. I have a GC but the electrical and plumbing work are being done by licensed electricians and plumbers working under the GC.

In California you can't have two devices operable at the same time because of water restrictions. My shower rough included a diverter which enables me to switch between the shower head and the handheld. Actually I have a three way diverter because I have a hand held installed close to the bench I built in the master shower. A diverter is somewhat like what people are familiar with in a tub/shower combo - in that configuration you turn on the water and it comes out of the bath spout or you change it to come out of the shower head.

That’s a Giant RED Flag. For the whole reason you posted your question. You should never have to search the internet to buy plumbing. Professionals are supposed to use their expertise to source and supply the correct products for their customers. They are not supposed to fob off product selection to a customer who then has to research everything and still doesn’t buy everything needed to do the job properly.

You don’t know what you don’t know. But the Pro does. Which is why they are the Pro, and why they need to control the materials sourcing.

I stand by my assertion that you need to delve a lot more deeply into the project specifics because you may be dealing with hacks.

My contract with my GC provides that I supply the fixtures and obviously the rough stuff as well since it has to work with the fixtures.

However, at some point someone who understands technical plumbing issues should be doing the purchasing or telling you exactly what to purchase. When I was selecting my shower fixtures, my designer obviously helped me with the look of the fixtures but she also explained the difference in shower valve temperature regulations - thermostatic versus pressure balance and then I decided which kind I wanted. The shower fixtures you select would then determine what rough you needed and she was responsible for ordering those. In other words I selected the style and how I wanted the end use experience to be like but she was responsible for making sure that everything necessary was provided to the GC so his plumbers could install what I wanted.

So although I was providing the fixtures to the GC, someone with technical expertise was guiding me in the purchase.