[Milsurplus] Identify again please, this headphone element?

[Hubert Miller]

Robert Downs - or anyone - please remind me what this earphone element is for. Comes in round cardboard box. Label reads:

GOVT ITEM No. 13
1 EACH 2B611  A/1 REC
ORD. NO-16038-PHIL-43
CONTRACTOR
AMERICAN AUTOMATIC
ELECTRIC SALES CO.
CHICAGO U.S.A.

When I bought these around 1985, I was told they had a high failure rate, no continuity, but - I have not found that to be the case.
( Not forgetting my aberration of a couple months back, when I mistakenly tested them as defective, but my test equipment had a problem. )

So are these for aviation headphone installation, high impedance ?
thanks-
Hue
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