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From the Toolbox – a reader-submitted parts question

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The anodized aluminum caps in question. 

It’s been a while since our last From the Toolbox segment, and this one comes to us from reader Dave Wood. Dave is asking for help identifying something that’s more of a part than a tool, but still fits in with the spirit of this series. Dave writes:

I have a mystery that perhaps you or your readers could solve. It is related to the video you published in your July 17 edition, entitled “Fuel Injection Systems Produced by Rochester Products.” My father worked at that plant during the 1950s & early 1960s on the fuel-injection project when it was being developed. I was a young boy at the time. Many nights he would bring home a handful or more of red aluminum caps for me to play with with my other toys. These caps are about 1/2″ in outside diameter and 5/8″ long. They have an internal thread that I cannot identify (close to imperial 3/8-24 or metric 9mm-1.00 but not quite these thread forms). I always wondered what part they played in the fuel-injection program. Possibly something a GM vendor had threaded on a component to protect it during shipping?

Terry McGean, Hemmings editor-in-chief and editor of Hemmings Muscle Machines, suggested the caps could have been used on the Schrader valve found on the fuel rail assembly, which is a 4AN fitting. The red anodizing on the caps seems to confirm this as a possibility, though the smooth sides would make them difficult to tighten, and difficult to remove with greasy fingers.

Rochester FI caps

Photographed with a pen to give a sense of scale.

What’s your take? Were they used to protect the Schrader valve during shipping and assembly, before being replaced by a knurled metal cap? Were they used on a different fitting relating to the Rochester fuel injection assembly? Are we completely off base on both theories?