Schrader valve details

[Tony Smith]

I have been buying replacement Innertubes for 11.00-20 tyres. There are relatively cheap Korean and Indian made innertubes getting around, but they are designed for Dual wheel applications on offset rims and have quite long valve stems. The valve stems are bonded to the tube and can't be easily changed. This is fine if I want to maim passers-by like Ben-Hur's Chariot, or rip the stems out on obstructions. But I don't!

A little more pricier, Michelin make a range of heavy duty truck tubes with replaceable valve stems. The "Standard" stem supplied with the tube is also a long one for Dual wheels (on the left in the pic below), but there are other sized stems available for Single wheel applications like the Blitz (the short one on the right is perfect for both 16" and 20" CMP wheels). Or at least there should be, but demand is low and the Michelin Importer does not have a lot in stock. In fact, it seems I got the last 2. But I do have a few of the stock "Standard" stems which should be able to be cut shorter and rethreaded for the valve.

Which brings me to my question. Does anyone know the thread sizes for the Internal thread for the valve unit, and the External thread for the cap? And the valve seems to seat against a taper within the valve stem at a fairly steep angle, would anyone know this angle, or are there tap and cutter kits available for this job?