As Mike,Dean, and Eugene stated the key evidently was removed from a Western Electric Telephone Test Set a 35F. A Yahoo search provided a photo of the set.
Z

On 11/8/2021 9:34 PM, W2HX wrote:

There was a telephone relay tester that had a key very similar to this.

Sent from Nine

From: "B. Smith" <[email protected]>
Sent: Monday, November 8, 2021 8:32 PM
To: Military Radio Collectors Association
Subject: [MRCA] Key Ident

Was going through my keys and found this. Anyone recognize this key. Is it military ? Does it mount on a small transmitter or miniature telegraph console? Very well made. Several adjustment screws and has a "shorting" switch and two long mounting bolts.
Z