I believe the high pressure stems have a coppery colored metal, with a rubber cover that ends partway up. When using TPM that screws onto the end of the stem, I always insist on ALL-metal valve stems, which are usually shiny metal (looks like stainless to me) with no rubber visible; the monitors can put a lot of side to side torque on the stem and weaken one that isn't strong enough. TST's website states, "The added weight of the sensor on a rubber valve stem could cause problems that will be avoided by using metal valve stems."