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Author Topic: What size tap - any plumbers?  (Read 1613 times)

westybob

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What size tap - any plumbers?
« on: August 10, 2012, 07:59:35 PM »
Any plumbers or pipe fitters among us?
I want to fit two nominal 15mm bsp nipples to a catch can. What size tap do I need to cut the thread? I calculated that it needed to be 13/16 but there seems to be no such tap size. So is it 3/4in or 7/8in??

Nightslug

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What size tap - any plumbers?
« Reply #1 on: August 11, 2012, 03:23:32 AM »
Yeap, should be 1/2 inch/15mm dude (nominal bore) plumbers terms
there will be a TND for it fore sure

westybob

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What size tap - any plumbers?
« Reply #2 on: August 11, 2012, 01:51:48 PM »
I need to know what size tap to buy e.g. 3/4 or 7/8 or other??!

GTS4R

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What size tap - any plumbers?
« Reply #3 on: August 11, 2012, 08:50:52 PM »
Could be 3/8 bsp if it is around 15mm, or could be 1/2bsp depends what you mean by nominal, either nominal bore or the nominal size.


It will either be 3/8 or 1/2bsp not 100% sure what you are working with tho, if the nipples you have are around 16.5mm on the outside of the thread it will be 3/8bsp if it is bigger 20mm and over it will be 1/2bsp.
« Last Edit: August 11, 2012, 09:29:08 PM by GTS4R »

westybob

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What size tap - any plumbers?
« Reply #4 on: August 11, 2012, 09:46:17 PM »
Clearly you guys are not plumbers! Its called a 15mm nipple and its  1/2in BSP I know that much. The bit I don't know is what size tap (as in tap and die) I need to cut a thread so that I can screw the fitting in!!!

GTS4R

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What size tap - any plumbers?
« Reply #5 on: August 11, 2012, 10:41:44 PM »
Well you were kind of confusing in your first post and missed out the 1/2 in front of the bsp, and had 15mm bsp.

If it is 1/2BSP you will most likely need a 1/2 bspt tap.


Is this what you are playing with??

http://www.megaflex.co.uk/components/com_virtuemart/shop_image/product/9fb772f5912bf988d9558d077ffc6855.jpg
« Last Edit: August 11, 2012, 11:08:11 PM by GTS4R »

westybob

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What size tap - any plumbers?
« Reply #6 on: August 12, 2012, 12:23:44 AM »
Thanks for trying! Confusingly the trade uses metric terms to identify things that are still imperial so a plumbing fitting which is called a 15mm nipple is actually 1/2in BSP which derives its name from a loose association with the diameter of the pipe it is supposed to contain and the nipple is actually 20.95mm OD. I have found the drill size for the tap which is 19mm so the tap size will be a little more hence my guess of 13/16 which doesn't seem to exist so I'll go to a tool store tomorrow and try a 7/8 in  tap.

We have the English to blame for this nonsense and the rest of the world for not completely adopting the SI or metric system!!!
« Last Edit: August 12, 2012, 12:25:05 AM by westybob »

GTS4R

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What size tap - any plumbers?
« Reply #7 on: August 12, 2012, 08:15:39 AM »
Ok got a photo of the nipple you are using? i'm keen to see what you are using, have you had a look/google at a drill and tap chart? or can you take the nipple with you and match it to a tap.

gtsr

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What size tap - any plumbers?
« Reply #8 on: August 12, 2012, 08:21:24 AM »
They use 15mm (where hose goes) barbed nipple with 1/2 BSP thread. At least that's how I've seen it listed when buying barbed nipples.

As far as I know, taps can be used for UNF/UNC/NPT threads.

Plumber probably would tell you to use a Union (hose adaptor) with a 1/2 BSPF (BSP Female) thread on inside to 7/8 UNF Male thread.

downtrail

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What size tap - any plumbers?
« Reply #9 on: August 12, 2012, 09:58:30 AM »
Quote from: westybob;603621
Clearly you guys are not plumbers! Its called a 15mm nipple and its  1/2in BSP I know that much. The bit I don't know is what size tap (as in tap and die) I need to cut a thread so that I can screw the fitting in!!!

first you need to know if its a tapered BSP thread or not I will assume it will be tapered if its a nipple as i havent seen a straight bsp thread for a long time.

You have answered your own question. if the thread size is 1/2" bspt then you need a 1/2" bspt tap.

Bspt mean brittish standard pipe taper. and pipe is measured from the inside diamater as where tube is measured from the outside diamater.

Bspt thread is tapered so just getting a std tap will not surfise as you will not get the taper with it.

drill size for 1/2" bsp is 19mm 0r 3/4"
drill size for 1/2" bspt is 18.25mm  or 23/32"
« Last Edit: August 12, 2012, 10:26:45 AM by downtrail »
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westybob

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What size tap - any plumbers?
« Reply #10 on: August 12, 2012, 12:30:20 PM »
You're right it is a tapered thread. But I have already spent some time in the second hand tool shops looking for a BSP tap with no luck so may have to try a 7/8 tap which looks about the right size.

Thanks for everyone's suggestions. The problem only arises because where I am currently boarding I have no garage let alone workshop - my other catch can I took to a fabricator to weld on a couple of proper outlets and this one I was trying to do on the cheap with a couple of nipples I already had. Will probably end up more expensive time wise but I'm nearly there now so I may as well persevere!!
« Last Edit: August 12, 2012, 12:32:43 PM by westybob »

downtrail

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What size tap - any plumbers?
« Reply #11 on: August 12, 2012, 01:00:39 PM »
You will have to goto an enginnering supplies shop. such as waitamata hydrolics AES etc to get the right tap. I wouldnt bother using anything else it'll just turn into a mess if you really dont want to spend money on the right tap go down to an enginnering shop and ask them to run a tap through go hydrolink I know they have a bsp tap set there (from memory)
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gtsr

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What size tap - any plumbers?
« Reply #12 on: August 12, 2012, 07:03:26 PM »
If don't have a workshop and only have a drill, the Union in link below should work.

Bulkhead Union with lock nut -

http://www.brassfast.com/bulkheadconnectors.htm

It's usually available from a plumbing supply store (may find it hard to get 1/2 BSP thread in store, as probably not a commonly used / stocked part, so have to order it in). From what I understand, it's for mounting bsp thread barbed nipple to walls of tanks, etc. You'll need a Oring, gasket or tape to seal thread to body of catch tank if it's round or flat walled.

base

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What size tap - any plumbers?
« Reply #13 on: August 12, 2012, 08:26:10 PM »
go to the hose doctors and take the fitting with you they will have the right tap think i paid like 30 for a 1/2bsp one

Lobster

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What size tap - any plumbers?
« Reply #14 on: August 23, 2012, 11:39:24 PM »
This thread is so confusing...Buy/borrow the correct 1/2 bspt tap. Drill an 18.25mm hole. Run the tap through it.

Why are you looking at 7/8, 3/4 or 13/16 unless your asking about drill hole size??? A 7/8 (or any of those sizes) tap won't work at all, its nearly twice the diameter of your fitting. A 1/2 bspt tap will.

 As for finding one, did you try a hydraulics/engineering shop? Waitemata Hydraulics would be the easiest for you..