New Radiator Vent Won't Fit

Brycewvu

I'm trying to replace a Hoffman that is stuck open with a maid o mist and when I try to thread the MoM into place, it's not catching. Other Hoffmans work that I took from another radiator. I was thinking I can just use a tap to clean things up but don't want to make assumptions on the correct thread size. Can you guys point me in the right direction so I don't blow out the threads on my radiator?

Also, other MoMs fit in the threads from other Hoffmans around the house. 

ethicalpaul

You can drill and tap it to 1/4" then reduce it back to 1/8" or use a 1/4" vent.

Or you can wrap some teflon tap around the vent threads to see if that gets you there

Brycewvu

Sorry I didn't clarify before. The MoM is too big and doesn't fit.

EBEBRATT-Ed

Something seems out of wack. All radiator vents are 1/8" IPS in most cases.

ethicalpaul

Oh ok sorry. Does this non-fitting MoM fit in your other radiators?

MoM vents do come in 1/4" variants I believe. Make sure you don't have one of those.

Intplm.

If the pipe size mentioned is correct. Go get a 1/4 x 1/8 inch bushing and install it.

BobC

Years ago i bought 3 MOM radiator vents and two of them would not fit, they seemed the right size but just would not engage the thread. It tuns out the two bad vents had straight 1/8" threads instead of the NPT threads they were supposed to have. The NPT threads have a taper that straight threads don't and without that taper they wont catch.

I picked up a 1/8" NPT Die and put the correct thread on them. Assuming the vebts you have are not the somewhat rare 1/4" typw, either return or get a die and fix them.

Bob

Brycewvu

I know its been a while but I wanted to give a final update on that difficult vent. I had someone come out and take a look at it and there was a piece of an old vent stuck in there! They tapped and cleaned everything up and now it works great!