Headspace Gauges

I´m a German cartridge collector (Member of the ECRA) and one subject of my collection is military issued headspace-gauges.
Recently I purchased a nice set of headspace gauges with a wooden box for storing it. The set consists of 10 pieces. Each place of a gauge in the box is inscribed with
numbers. These numbers ranging from 1.555 up to 1.564. As I have an amount of other gauges, I persume, that these gauges are made for weapons in the 7.62 Nato
caliber. If I convert the numbers into the metric system, I will achieve similar or same dimensions for headspace as shown on my german gauges.
From literatur regarding US-GI .30 Go-NoGo gauges, I know, that there is a certain drawing-number and gauge-number assigned to each gauge or gauge set.
In the case of the .30 gauges, the drawing-number is C7719 and the gauge are ranging from index A to S.
All the gauges are inscribed in the same manner described belowe:
“SAP G-455”; “CHAMBER”; “D-7162891”; “HEADSPACE”; “C-1.555” (this number is changing from 1.555 up to 1.564); a number “S-XX-XXX” (the “X” are numers like
S-53-337 for example).
There are slight differences in the order of appearance or there are slight add-ons like “OP HEADSPACE” or "D-7162891 OPER.

Is there a specialist in these subject, who can give me more information about this set.
For which weapons is it used for?
Are thy headspace gauges for maintainance or or the manufacturing process?
Who made these “SAP” = Springfield Armoury???

I would appreciate all information or drawings I can get (not only answering the questions above), regarding these gauges and the use of it.
Furthermore, I´m interested in all kind of military issued headspace-gauges no matter of the caliber. All information is welcome. Can also trade some (send email
for contact).

I´m sorry, that I don´t post picturesat the moment, because I´m not so good in computers! If somebody wants to see pictures, I will try to put some into a file
at “Dropbox” later on.