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Left hand thread on cast iron rads?

JimRaffertyJimRafferty Member Posts: 19
Over the past year we've worked on a couple of old cast iron rads that required left hand threaded bushings.
We tracked down the parts and got the repairs done, but I'm trying to come up with a reason why left handed threads?
Or were the Dead Guys just trying to mess with our heads?


  • kcoppkcopp Member Posts: 3,468
    They were prob made before the day that unions were made. Same goes for left/ right couplings.
  • Jamie HallJamie Hall Member Posts: 12,719
    Depending on where in the radiator they are, I can think of at least one good reason: if you have a nipple connecting two relatively hard to rotate objects -- such as a piece of a radiator (or the whole thing!) or a valve connected to a riser or what have you, if the nipple has one left hand and one right hand thread turning it one way will pull the two objects together, while turning it the other will spread them apart or separate them completely.

    Or it may be to mess with your head, like Chrysler corporation cars in the '50s, which had left hand thread wheel nuts on one side and right hand on the other...
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • JimRaffertyJimRafferty Member Posts: 19
    Thanks, but the left thread tappings are on the opposite ends of a free standing floor rad. We could crank the bushing in left, the rad valve spud right and then the rad valve union right.
  • New England SteamWorksNew England SteamWorks Member Posts: 1,352
    I have also encountered left threaded radiators. Always a head scratcher until you realize what's going on!

    New England SteamWorks
    Service, Installation, & Restoration of Steam Heating Systems
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