Early TPMS sensors came with non-replaceable metal valves. Whenever a tire is serviced, a new service kit should be installed onto the valve to replace worn-out components (nut, grommet, cap & core).

Later sensors came equipped with replaceable rubber valves. The rubber stems on snap-in sensors should be replaced during tire service.

Initially only a couple styles were available, but now there’s many stem types for the various sensor manufacturers. Different sensors = different shapes for valve ports.

Shops that stock both service-kits (for clamp-in sensors) and a few different rubber valves (for snap-in sensors) will be able to service OE sensors on most vehicles.
Therefore it’s recommended to keep a few different rubber valves in-stock, for the various TPMS-sensor styles that are now available in the market.

Information on Alligator’s TPMS-valve offerings can be viewed here. And the TPMS catalog has additional details, including info on service-kits for OEM sensors with metal stems.