All towed motorized vehicles (cars, trucks and SUVs) will have either rubber (brass) or metal (aluminum) valve stems. If you have a rubber valve stem, you will need brass transmitters. If you have a metal valve stem, you will need aluminum transmitters.
RVs, Motorhomes, 5th Wheels and Trailers will all have either rubber (brass) or metal (steel, chrome, or nickel) valve stems, all of which work with the TireMinder brass transmitters.
All TireMinder kits come with brass transmitters. If you need aluminum transmitter for your towed vehicle, they can be purchased separately.