it is a finish standard of valve flanges
WCC mean standard temp.
valves are available in three types first is full bore equal to 100 percent opening normal bore/port equal to 80 percent opening reduced bore equal to 60 percent opening
npt, national pipe thread, is a standard for threads on a screw. I (not a plumber) don't believe "npt valve" makes sense , but probably refers to a valve which has npt threading. Yes, a NPT Valve would be a valve with pipe threads as opposed to a sweat valve which has solder connections. There are several other type of piping connections too.
I would say because there has to be a standard method of installing flanges that everyone needs to follow. For the simple reason when installing or replacing items such as valves with welded or otherwise fixed flanges, if there was no standard the replacement valve would be 1/8 of a turn or 45 degrees off center if the piping flange bolt holes were on the verticle and the valve flange bolt holes were not. This would be in the case of 4 or 8 bolt flanges.Also in the case of non flanged valves where long bolts pass thru both flanges and squeeze the valve to make the seal a vertically placed bolt hole would interfere with the valve operator or handle preventing the valve from being mounted straight up, down or horizontally.
The standard length of a presta valve is typically 42mm.
The standard valve type for a 700c bike tube is called a Presta valve.
it is a finish standard of valve flanges
A standard trumpet typically has three valve numbers.
469.4 * 10^3
The standard diameter for a Presta valve on bicycle inner tubes is 6mm.
The standard presta valve size for bicycle inner tubes is 42mm.
The standard diameter of a Schrader valve used in bicycle tires is 8.5 millimeters.
The standard size of a Schrader valve used in most bicycle tires is 8mm in diameter.
The standard valve stem hole size for most valves is typically around 0.375 inches or 3/8 of an inch in diameter.
WCC mean standard temp.
+/- 5% of setting