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My tub's drain flange has had the little cross piece inside it broken out, which means I cannot screw a grid drain into it. Right now, it's totally open and an invitation for my toddler to drop stuff down. Not to mention lots of hair, etc.

I believe I need to replace the drain flange and put a grid drain on top of that (I want a grid drain like a shower instead of a typical tub stopper).

"Drain flange" terminology from this image.

"Drain flange" terminology from this image.

I have measured the diameter across the drain at just under 2" which I believe means a pipe thread size of 1.5" (from http://www.plumbingsupply.com/pipethreadsizing.html). However, I thought I remember learning that drains may be either coarse or fine threaded.

Before removing existing drain flange, is there any way to know if it is coarse or fine threaded, or are all 1.5" drains the same as far as thread count goes? I want to be sure to order the correct part, whether I do the work or hire a plumber.

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I have never come across flanges that weren't compatible, and haven't seen manufacturers specify TPI on their kits or replacement parts. There are plenty of oddball pieces here and there but upon coming across those (on rare occasions), I'd be replacing the entire assembly.

There is really no way to know the TPI without removing the flange, but chances are you will be dealing with coarse threads.

  • There's probably an American vs Metric thread version of these things. Not likely to be a problem if you buy in the tub's country of origin. – Wayfaring Stranger Nov 11 '13 at 18:00
  • i'm accepting this answer because it seems perfectly reasonable...though I know it's not particularly authoritative – susie derkins Dec 20 '14 at 17:14
  • There are different thread pitches I have run into this on acrylic tubs that come with a drain kit. Purchased a replacement because the chrome was peeling and the size was correct but the pitch was not the same. – Ed Beal Feb 19 at 22:05
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For the record, there ARE different threads. I just bought a new flange (only one type was available for sale in my neighbourhood) which did match the thread count on the existing drain shoe. Particularly annoying in that I was unable to purchase a new drain shoe.

Actually, the drain shoe is what I was really trying to purchase as the existing one had broken. I only bought the new flange only because the old one suffered mior damage to the cross piece during removal. In the end, I had to clean up and repair the old drain shoe and then reuse the old flange.

Caveat: My house is over fifty years old, and the drain shoe and flange in question are probably of similar vintage.

  • ... did you mean "which did not match the thread count on the existing drain shoe"? – Daniel Griscom Jun 18 '16 at 10:11
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Use a thread TPI tool that comes with a tap/die set to find the correct TPI, and yes they can be different depending on age of the tub/brand/style.

  • That's the perfect way to measure it. In my case, I had a flange with a different size and thread, I had to buy a thread adapter to fit a flange with another different thread. Very rare, but everything worked out. – riseagainst Mar 22 at 19:29

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