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Threading on glass gauge nuts? (or are sight-glass related specs a secret?...)

Jim_NY
Jim_NY Member Posts: 51

Been doing my own steam-boiler sight-glass cleaning/replacement for years. Just helped a neighbor do it for the first time. We both have 5/8ths glass.

Making conversation, he asked, "so what kind of threading is on these things" (the glass gauge nuts). Other than that it's "standard" - never thought about it. And even though I know it doesn't matter, unfortunately now I'm curious.

My best-est web-search terms couldn't find anything. A couple of tries at online customer service of suppliers accessible to non-professionals, only got back "it's standard."

With my bad eyes, looks like near to ~20 TPI, with a ruler near to ~7/8" - and since it uses a gasket, may be straight thread...?

It would be too much of a coincidence if it turned out to be the kitchen-faucet aerator "standard" (which one website said is 15/16"M 55/64"F -20 UN thread). But would guess it's at least close.

Thanks.

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