I need to re-tap a vent hole, I think? Confused about size

SethK

The vent isn't threading into the "new" radiator I just painted. There doesn't seem to be paint or much rust on the threads, but they look pretty rounded over at the opening, they may have been sand blasted off. I can almost thread a vent in but I think it is cross threading and popping out. I assume I need to re-tap.

I see about 50 threads on how to retap a thread hole with a 1/8" 27 thread/inch NPT tap or something. I would ask in one of them, but they are all locked...??

The hole is 3/8". I guess it's for a 1/4" ID pipe, but why do I need a 1/8" tap? Are taps measured by ID radius? If it is 1/8" in diameter that seems like it would just slide through the hole and end up inside the radiator.

Anyway, I went shopping at Home Depot and they had a bazillion taps, but none of that size and not were 27 threads/inch. I think I saw 28, or 26, but not 27.

I went shopping online but the pictures don't show the size, and I don't want to spend $30 and get something that can only tap a 1/8" hole.

Very confused, please help. Thanks.

JohnNY

You should be looking for nominal size ⅛" NPT. That's all you need to know.

Look:
https://www.grainger.com/product/WIDIA-GTD-Tap-1TRH7

KC_Jones

1/8" pipe is .405" OD. The tap you are looking for is a pipe tap which is tapered. The ones you saw at big box (judging by thread count) are standard machine threads for bolts.

Taps are size specific, so if you buy one it will only be able to do 1/8" pipe. Here is a link to one, I am not advocating for brand or anything just showing you what you are looking for.

https://www.amazon.com/Vermont-American-20371-Carbon-Steel/dp/B000K1LZ76

ChrisJ

As others have said, 1/8" NPT which I believe is 27 threads per inch. Most specify a size Q drill bit.

If you google "1/8" NPT pipe tap" you should find plenty of options.

When you run it in, don't go all the way, go in some and as it bites, back it out a little then go in further. After it chases the threads check the tightness with a vent. It's a tapered thread so the deeper you run the tap in, the further the vent will thread in and it's best not to go too far. This way you can always run the tap in further down the road if the threads need help.

I like 3 or 4 turns until tight on a vent my self.

Hap_Hazzard

Before you tap, clean and chase.

If you can't screw the vent in straight, it would be risky to try to screw a tap in. If you cross-thread the tap you'll be in real trouble.

Pick up one of these: http://www.homedepot.com/p/3-in-1-Radiator-Valve-Repair-Tool-B8610/202246291 and a wire brush just big enough to fit snugly in the hole.

If there's paint around the lip, cut it away with a utility knife, then push the wire brush in and twist it out, then blow out the loose material with compressed air. Carefully screw the thread-chaser into the hole until it feels tight, then back it out, and blow out the loose material and clean the chaser. Repeat until the threads are clean and no more black stuff comes out. Then tape the vent fitting and screw it in.

Pumpguy

It is often recommended to use a lubricant when cutting threads in metal. The usual recommended lubricant for cast iron is kerosene, although today there are many commercial cutting fluids available.

I just use a light spray of aerosol penetrating oil on the tap when threading cast iron. Try not to get any oil inside the radiator.

SethK

Thank you everyone for your help. I swung by Home Depot, bought that tool and used it as you guys describe. The tool seemed really light, but it threaded itself in as I went forward and back, but every time I tested with the vent it still wouldn't thread. After a few tries with the home depot tool I looked at it and saw it was stripped smooth.

So that's going back to the store, and I'll be ordering one made out of steel from Amazon. Thanks for the help everyone.

ChrisJ

A Home Depot tool that didn't work correctly?

Naa.........can't be!

Pumpguy

I'm sure Home Depot has a real 1/8" NPT pipe tap.

I've never seen the threads on a pipe tap strip smooth. I've had a few where one thread on one land of the tap get chipped off when tapping real hard metal, but never totally strip smooth.

Hap_Hazzard

I should apologize for using that link. I just wanted to find a picture of one; I didn't mean to recommend home cheapo.

After you return it, wait a couple days then go back and check the shelf where you found it. Odds are it'll be right back there waiting for another sucker.

SethK

I figured it would be junk, and the one review it had was 1 star, but I figured that it would work well enough to fix one radiator and save me from waiting for an online order. Nope.



Do I need to use a tap wrench with a tap?

Tinman

I can get Milwaukee, Klein, Ridgid, Diablo, and others at HD if I happen to be in there and need to get it now.

All solid tools.

We make an effort to go a bit out of our way to get all our tools from Berland's Tools though. 3 branches in the Chicago area.

Tinman

A double handle tap wrench gives you a better chance of a straight thread. If I'm just chasing threads, I'll go as far as possible by hand and then use a crescent wrench if it's needed.

BobC

Use a 1/8-27 NPT tap and don't go to deep, you need the taper. Any decent hardware store should have one.

https://www.amazon.com/Vermont-American-20371-Carbon-Steel/dp/B000K1LZ76/ref=sr_1_1?ie=UTF8&qid=1476791787&sr=8-1&keywords=1/8+27+npt+tap

Bob

ChrisJ

Stephen Minnich said:

I can get Milwaukee, Klein, Ridgid, Diablo, and others at HD if I happen to be in there and need to get it now.



All solid tools.



We make an effort to go a bit out of our way to get all our tools from Berland's Tools though. 3 branches in the Chicago area.

I'm always extra cautious with this.
More often than not, name brands sold at these stores (Homer, Lowes) are some how cheaper made than from other places.

I haven't seen this with their tools yet, but with plumbing fixtures, garbage disposals etc I have. My 15 amp Milwaukee Sawzall came from Homer and actually, I went for a cheaper one but they couldn't find it so I got a free upgrade to the bigger one assuming I wanted it, which I did. As far as I know, it's the real McCoy and in no way different than any other. But I'll always research it before just buying from them.

Their Insinkerator products are one of the items I found they do this with. I think only the absolute top model is the one that isn't changed. All others have things different, such as plastic grind chambers etc.

SethK

The problem with name brand tools with a great reputation is that reputation is worth a lot more than the company to large competitors. Black and Decker had a great reputation, they were bought out, now they sell cheap Chinese junk. The Stanley Black and Decker company also owns Dewalt and Porter-Cable which seem to be the exact same tools in different colors. TTI owns Milwaukee, Ryobi and Rigid (I love my Ryobi tools, btw).

Anyway, I bought a tap wrench, hopefully it helps.

But I fear something else is wrong that I don't understand. With the HD tool is seemed like the threads were fine, but I just could not get the vent to start threading in. It seemed like the vent pipe was a little bigger than the HD tool, I'm hoping the tap I ordered is larger. Or maybe something else is wrong and I'm making things worse...

ChrisJ

SethK said:

The problem with name brand tools with a great reputation is that reputation is worth a lot more than the company to large competitors. Black and Decker had a great reputation, they were bought out, now they sell cheap Chinese junk. The Stanley Black and Decker company also owns Dewalt and Porter-Cable which seem to be the exact same tools in different colors. TTI owns Milwaukee, Ryobi and Rigid (I love my Ryobi tools, btw).

Anyway, I bought a tap wrench, hopefully it helps.

But I fear something else is wrong that I don't understand. With the HD tool is seemed like the threads were fine, but I just could not get the vent to start threading in. It seemed like the vent pipe was a little bigger than the HD tool, I'm hoping the tap I ordered is larger. Or maybe something else is wrong and I'm making things worse...

What brand vents did you buy?
Are they Maid O Mist?
I recall something about a run of MOM vents having the wrong threads on them a while back. Not sure if it was ever fixed, but maybe even if it was, you found an old batch?

SethK

Yes they are MOM. The first one I tried didn't fit, but easily screwed into another radiator. I bought a second one and it also isn't screwing in.

The only difference to my eye is the hole on the radiator that it screwed into has nice 90 degree edges at the opening, while the problem radiator has rounded over edges.

BobC

I posted something a couple of years ago about a couple of MOM vents that didn't have a taper. I ended up buying a 1/8 NPT die to recut the threads. here is a link to that thread -

http://forum.heatinghelp.com/discussion/144079/bad-threads-on-maid-o-mist-vents#latest

Bob

Koan

Hi - I have an idea or two, or several. Hope something helps.

First and foremost, verify you are screwing into the correct thread size. Looking at the home depot pot metal tool, those threads are shot. Could it be that this radiator is threaded differently??

If the new MOM vent fits an existing hole in another radiator, but the existing vent won't fit the new radiator hole, either the threads in the new radiator are bollixed or are a different size.

Maybe go to the hardware store and find a brass 1/8 NPT pipe nipple. You can see the taper and compare to the threads on the new MOM vent. Next find a fitting the will fit onto the 1/8 NPT pipe nipple, it will have 1/8 FPT (female threads). see how easily it screw onto the pipe nipple. See if that will screw onto your new MOM vent.

This has the advantage of not assuming all your radiator vents are threaded the same.

If you do rethread - get a decent tap from MSC - not a hardware store carbon steel job.

Here is a link:
mscdirect.com/product/details/04662029

Make sure you sure your time, use some threading oil on a rag. start the tap, back it off and wipe it with the oil soaked rag, then back in.

First and foremost, verify you are screwing into the correct thread size - I have a funny feeling they may be tapped to a something other than 27TPI.

Good luck!

ChrisJ

The good news is if the current threads are small, a size Q drill bit + a good 1/8" NPT tap will fix the problem(s).

If you can't do that because there's not enough metal, a 1/4" NPT tap and I think, 7/16" drill bit and a nice chrome plated 1/4" to 1/8" bushing will make things right and not look bad either.

My point being, no matter what, we can help you make it work and it'll work well for a long time.


I bought all of my stuff from McMaster-Carr.
A bit pricey at times, but they generally carry really good stuff. I bought my taps and handle from them. For the 1/4" I use a ratchet and a socket that fits over the square end. They also have the 1/4" NPT to 1/8" NPT plated bushings that look good.

SWEI

Stephen Minnich said:

We make an effort to go a bit out of our way to get all our tools from Berland's Tools though. 3 branches in the Chicago area.

Copper State Bolt & Nut for us. It's a three hour drive to their closest branch, but they do repairs, too -- and thanks to the mine, they deliver here twice a week. It's really great to have vendors we can work with. Wish we had more supply houses that ran trucks here.

Koan

@SWEI @ChrisJ @Stephen Minnich
My point was that a pipe tap is one of those items where quality really matters and it is worth spending a little more.

SethK

BobC said:

I posted something a couple of years ago about a couple of MOM vents that didn't have a taper. I ended up buying a 1/8 NPT die to recut the threads. here is a link to that thread -

http://forum.heatinghelp.com/discussion/144079/bad-threads-on-maid-o-mist-vents#latest

Bob

That's interesting, because I tried to screw the MOM vent into the Home Depot tool and it would not, not even close. I figured the tool was crap but maybe the vent wasn't tapered...

Anyway I ordered one of the nicer looking taps on Amazon, made in USA (high speed steel I think), and it arrived, but the tap wrench didn't. I'm impatient so I screwed it in by hand then used pliers for the last few turns and the vent screwed right in! Thanks for the help everybody!

Hap_Hazzard

It's actually safer to start it by hand because you can't do any damage by cross threading. Tap wrenches are actually a little tricky to keep perfectly straight while you're turning. And the pliers shouldn't hurt the tap. If they did, return it. Taps should be harder than any other tool in your toolbox.

Koan

glad i t worked out!

Dave0176

Don't forget the Tap Magic

https://www.zoro.com/tap-magic-cutting-oil-16-oz-squeeze-bottle-10016e/i/G2336031/?gclid=CLfChZTj9M8CFVVahgodOJQJ9A&gclsrc=aw.ds