[Milsurplus] WWII stock number

[Glenn Little WB4UIV]

I have a dial glass from 1943.
Part number A-55F-2837.
STK-NO-2Z4990-21.
Contract NO. W-2279-SC-460.

In the box is a clear glass circle 5" dia.
This is 0.25" thick ans appears to be safety glass.

There is a second glass disk in the box.
It is 4.5" dia and 0.125" thick.
There is a one inch dia hole in the center of this disk.
Below this hole is "ZERO ADJUST".
Above the hole is a vertical red line.

I will try and take a picture.

Any ideas as to what this was used in?

Thanks
73
Glenn
WB4UIV

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Glenn Little                ARRL Technical Specialist   QCWA  LM 28417
Amateur Callsign:  WB4UIV            wb4uiv at arrl.net    AMSAT LM 2178
QTH:  Goose Creek, SC USA (EM92xx)  USSVI, FRA, NRA-LM    ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"