I'm not familiar with that either, but my guess is it's original to the truck. (assuming the truck is a GMC)

Have you looked in the old parts book?
For chevy http://chevy.oldcarmanualproject.com/1929_54chevyparts/index.htm
For GMC ??

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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