Thread on bicycle pump

[LeeElms]

Sorry, not actually metalwork at all, but I thought people here would know most about threads! (Please let me know if there is a better place to post this)

I am interested to know what the thread is that joins the hose to the body of a bicycle pump (pictures below). The outer diameter is close to 13mm, so I wondered whether it is 1/4" British Standard Pipe Parallel Thread, but that has a threads per inch of 19, which is a pitch of about 1.33mm, rather than the approx 1.64mm that I have measured.

Any ideas?

 

[RichardG]

Useful tables of most threads here.

Thread Identification

Looking at the British table 1/2 inch BSF is close at 12.7mm dia and pitch of 1.59mm?

 

[LeeElms]

I agree 1/2" BSF is close, but I don't think it is quite what it is -- the diameter is significantly larger and the pitch smaller.

But surely it is some standard thread?

 

[porker]

Sorry if you already know this but bicycles have a specific thread BSC. Not sure if modern bikes still use this but charts are available online

 

[LeeElms]

I've looked at the charts, but there isn't anything like the thread I'm interested in.

 

[Spectric]

I am interested to know what the thread is that joins the hose to the body of a bicycle pump

There is no standard but bsp was common. Another thing to watch out for are non standard threads which can be found on some imported goods and you just will not match or it may be an American thread such as NPS or national pipe straight , there is also the national pipe taper. For 1/4 & 3/8 NPS the pitch is 1.4111 mm.

Sorry if you already know this but bicycles have a specific thread

This was 26 TPI and used on British motorcycles.

 

[LeeElms]

Thanks for all the info. Still can't find a match in any of the charts mentioned. I think it's a 'non standard thread which can be found on some imported goods'!

 

[J-G]

... I think it's a 'non standard thread which can be found on some imported goods'!

There are very few items made with 'NON Standard' threads - they are usually used to maintain some leverage as far as future spares sales are concerned. Totally counter-productive though.

The first post mentions 'about 13mm' which is very close to ½" (12.7mm) and a 'measured' pitch of 1.64mm - which is very unlikely to be the true pitch since it translates to 15.4878 tpi - very difficult, if not impossible, to actually machine. It is much more likely to be 16 tpi which is 1.5875mm.

The item appears to be made from a plastic therefore the thread will be molded and consequently likely to be quite a 'loose' tolerance and there are only three pitches across which to measure. With the best will in the world I would not be confident enough to measure 4.92mm over those three crests (which is what 1.64mm would be) compared to 4.76mm (16tpi), unless I had a 50:1 shadowgraph image to view.

The bottom line for me is that I suggest that ½"BSF is highly likely and would try to find a nut of that size to at least test the fit.

Although ¼" BSP is 13.157mm nominal O/D (close), the pitch is 19tpi which is 1.3368mm so that is unlikely - unless the 1.64mm is an error and is in fact 1.34mm (ish) - that would be very close to 4mm over the three crests.

 

[LeeElms]

It does look like 1/2" BSF is most likely. The reason why I didn't think it was is that 'about 13mm' is around 13.1mm across the threads, and I assumed that a 1/2" would be a little less than 12.7mm.

 

[Inspector]

Any chance it is a "special plastics thread" or a proprietary one rather than one made for metal?

Pete

 

[Alpha-Dave]

Have you checked the diameter in multiple cross-sections of the threaded shaft? Given that it is likely moulded plastic, it can easily distort either during manufacturing (if it is a cheap part without proper thought for cooling after moulding), or it could have distorted during use if it was squashed at some point.

 

[LeeElms]

Pete: could be proprietary ...

Alpha-Dave: just tried measuring different cross-sections, and there is quite a lot of variation, and the average is somewhat less than my original measurement across the threads; still seems to be rather more than 12.7 ...

 

[toolsntat]

Not sure what you want to do here but maybe you could form a "nut" or whatever to fit by using "polymorph" ?
Cheers Andy

 

[Alpha-Dave]

Ok, so what is your final goal here? I assume you are not wanting to identify the thread solely for historical purposes, and actually want to attach something to it. Therefore at this point I would get a 1/2” BSF fitting (as per RichardG and J-G’s posts) and try it. If it doesn’t fit then sand down the high spots. If you’re feeling extravagant then get a die 2nd hand from ebay and cut the threads to an accurate 1/2” BSP.

 

[LeeElms]

I want to make an extension 'tube' - i.e. fittings and some flexible tubing. I have tried a 3D printed 1/4" BSP 'stretched' to the measured pitch, and with a rubber washer, it works quite well. But I was wondering if I could buy a proper part.

Alpha-Dave: not normally extravagant, but I'll have a look at e-bay. (I assume you meant 1/2" BSF at the end of your comment).

 

[Spectric]

Another suggestion, take it to your local plumbers and try some of their fittings, you may find something that will go on even if it needs a little sealant.

 

[J-G]

...and I assumed that a 1/2" would be a little less than 12.7mm.

That would be my opinion too - except --- we are dealing with a molded plastic thread so all bets in that light are 'off' As I said before tolerance on molded plastic threads is - - - - - plastic!

The idea of using a 'die' is certainly worth pursuing. Tracy Tools have a ½"BSF Die-nut at £6 - it's carbon steel but perfectly good enough to cut plastic - and you won't need a die-stock to use it, just a spanner --

1/2" X 16 TPI BSF

That link will take you to the specific page where you can click on the [Options] and select from the drop down list.

You might even find some success by getting a ½" BSF nut and filling three slots in the threads with a 3 square file - taking care with the orientation of course.

 

[LeeElms]

Thanks again for the suggestions. Quite busy at the moment, so might take a little while to progress this one ...

 

[Nelly111s]

Do you know the manufacturer of your track pump? They may be able to help?

 

[sploo]

That looks an awful lot like a Topeak Joeblow Sport, so I attacked mine with a thread checker. It's not UNC 1/2-13, and definitely not 1/2-20. The thread pitch is close to M12-1.5 (measured around 1.55mm pitch), but the external diameter of the threads is close to 12.9mm (which is larger than even a 1/2" UNC bolt).

M13-1.5, or 33/64-16?!

Maybe an email to Topeak is required (but do let us know the answer)!