Basically there are two criteria you have to get right. The size hole in the wheel and the cold pressure spec for the tire inflation.
For passenger and light truck wheels that use the standard "snap-in" rubber valves, you will usually find them to be either 0.445 to 0.461" or 0.618 to 0.633" dia hole. There is also a maximum metal thickness of 0.156" at the hole. Some aluminum wheels have special step machining to cut the thickness down to the proper dimension. Most steel wheels do not have this problem as they are thinner than 0.156" and run closer to 0.070". These "snap-in" have a 65 psi max spec and carry part numbers such as TR412, 413, 414, 418, 423 and the large dia. TR415 & 425. The difference is the total length which runs from 0.88 to 2.00 outside the rim surface.
AllTireSupply and you can order valves from them. I would never use any of these if I have a TPMS or on any RV.
The next group of valves are bolt-in metal and are rated for 200 psi. Now these are designed to fit the same wheel hold dimensions as the above passenger & light truck wheels. Some of these will come with two different size grommets so you can fit either diameter hole. Just be sure you get the correct grommet. These carry the P/N TR416 or TR416s for the small dia hole depending on which size wheel hole and these are about 1.4" long. This picture comes from MeyersTireSupply. They are a wholesale company in Akron, OH so you may need to get the name of a dealer in your area from the Meyers web site. They also have a 2" long TR416L. The nut torque on this type valve is 25 - 45 in-lb
There are also special High Pressure snap in valves rated for 80 or 100 psi cold set pressure
The 80 psi valves carry the P/N 600HP & 601HP at 1.2" & 2" long
The 100 psi 801HP & 802HP are 1.3 and 2: long
You will probably find these on new larger pickups .
Now we move to the big boys for larger "Truck/Bus" applications which for the RV owner means 17.5, 19.5 and 22.5 diameter wheels. There are some that are made especially for aluminum truck wheels but the standard bolt in valves are rated for 200 psi. These fit a hole dia of 0.618 to 0.633". These come in a number of lengths both straight and bent to 90°. Their P/N are TR500, 501, 570, 571, 572, 573, 574, 575. If bent there is a "c" suffix. The nut on these should be tight to 35-55 in-lbs
Now remember if you have aluminum wheels you may need special valves. The valves should use tire mounting lube on the grommets when installing. You should replace the rubber valves or rubber grommets whenever you change tires. I would squirt each valve with Windex or some spray cleaner and confirm it does not wiggle in the hole at least once or twice a year to ensure the nut is not loose and the grommet is still sealing properly.
Valves are only a couple bucks each so it is false economy to not replace them every time a tire is dismounted. Always use metal caps or TPMS sensors on the end of your valve stems to keep dirt of the core. If you have a lot of dirt or mud on the valve wash it off before removing the cap or TPMS..