Bill stated
the so called rubber that your not sure about are steel on the inside with a rubber coating on the outside
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Bill I beg to differ with you. The rubber valve stems that I was refering to were rubber except for the threaded brass sleeve that the core and cap thread into and over. The area that passes through the rim is rubber and that is where they broke. I said they because the one on the other tire broke when the tire store owner applied slight sideways pressure on it.
I was relaying my personal experience to alert people to a possible cause of some of the on going tire problems .
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Bill stated
Years ago the made a solid steel one threaded all the way down with a rubber seal then a round threaded nut to screw it down tight to the rim. I remember the rubber washers would deteriorate and the stem would fail. I have not seen these in 40-50 years
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Bill I'm really supprised that you have not seen any of them in 40 -50 years. That type valve stem is still made and they are used on many racing cars and heavy duty applications. They use synthetic washers now and have no problems with deterioration
Nick