As can be seen in the pictures below, there is no 'standard' spacing for the collars on the valve stem. While you need a micrometer to measure the differences in the distances of the collars closest to the threaded end, you certainly don't need any measuring tool to see the vast difference in the position of the collars at the opposite end of the stem.

The reason why there is no standard position for any of the three collars is because their positions are all relative to specifications or dimensions of the other parts of the valve, i.e. the valve leather, the valve button, the backing plate, the outside valve, etc., etc.) and the thickness of the gasket between the valve chest and the pouch board. Other things that need to be taken into consideration include; the thickness of the valve button and how many turns it is turned onto the stem when the valve is built. Generally, the button is turned on three complete revolutions. That way it can be adjusted 'in' or 'out' at least 1-1/2 revolutions (or approximately 0.100") to set the correct button-to-pouch clearance (or 1/16"). Then, depending on the thicknesses of all of the other components, the collars are spaced so that you achieve the correct valve travel (or approximately 0.035"-0.040").