Hope the dust caps arnt the cheap ones off ebay!!!
I bought some when I first got mine, was warned that you needed stainless ones or they would rust on. I put a bit of grease on the threads and it wasnt till one of the tyres looked a bit soft and I went to check the pressure, that I thought any more about them. (I know you should check weekly/monthly, but....)
The caps were well and truly stuck on, in the end I used mole grips to hold the valve and a spanner on the valve cap. Took quite a bit of effort to get them off.
Back to plastic dust caps now.
They did look good though.
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