# Presta valve threading



## restart (Aug 11, 2004)

I'm looking for the thread spec on the part of the Presta valve that screws into the valve stem. Basically I need to tap a short stem to fit an extender on it so I can continue to use the tubular tire. Thanks for any relevant info.
Mike


----------



## Mr. Versatile (Nov 24, 2005)

Whether or not the valves are threaded is indicated on the side of the box. All of the threadless valves I've seen have just a few threads to which you can fasten the extender. The threads on valve tubes are the same, so any will work just fine with your extender.


----------



## wim (Feb 28, 2005)

The external threads at the tip of both "threaded" and "unthreaded" Presta valves are M5 x 1.0 (very close to 24 TPI). The external threads on the main body of "threaded" Presta valves are M6 x 0.75 (close to 32 TPI).

/w


----------



## restart (Aug 11, 2004)

Thanks, guys. But what I need is a tap to thread the INSIDE of the stem on the tire. This one lacks threads and my extender won't screw in because there are no threads, so I have to cut some myself.
Carrying on....
Mike


----------



## danl1 (Jul 23, 2005)

restart said:


> Thanks, guys. But what I need is a tap to thread the INSIDE of the stem on the tire. This one lacks threads and my extender won't screw in because there are no threads, so I have to cut some myself.
> Carrying on....
> Mike


So, the threading for the valve core, right?

I take it you broke the valve off?

I honestly don't know the size of that threading, just trying to picture your problem.

Also, it might turn out that wim's answer is correct: the threading on the valve body might extend straight into the stem uninterrupted.Actually, that'd make a lot of sense. Unfortunately, I don't have removable-core tube handy to prove it.
(Edit: This is not correct. The body thread is finer than the 'cap' thread.) 



/edit: in searching for a better answer, I found this. At least you are not alone.

bottle cage bolts are M5x .8: you might compare the threads on your extender to those, just for a sense of size.


----------



## restart (Aug 11, 2004)

Yes, we are on the right track. The picture you sent is perfect. What I need is the threading on the part of the core that's right in the middle....it looks like there are 5 or 6 threads right in the center of the picture. That's the one I am looking for. Unfortunately, I don't have a metric thread gauge, but the closest I can by comparing with other bolts and using my caliper on the diameter is about 4.5mm diameter and .60 pitch. This is not a standard size, apparently. McMaster-Carr stocks a 4.5 x 0.75 tap, I wonder if that would be close enough?
BTW, I also found the thread on Cycling Crowd and sent a message to Mike Kennedy to see if he got any answers.


----------



## restart (Aug 11, 2004)

Here is a picture with an arrow pointing to the area of interest


----------



## wim (Feb 28, 2005)

I believe that's a DIN 7756 Vg5 thread. Not sure right now how to bring that across to U.S. or ISO standards, but a search on DIN 7756 (German Standards Institute) Vg5 (Vg = Ventilgewinde > valve thread) might get you the information on the tap you need. Also try "Sclaverand" in your search, which is another name for "Presta" [valves]. FWIW, here are the details on DIN 7756 valve threads.
http://www.gewinde-normen.de/en/valve-thread.html


----------



## danl1 (Jul 23, 2005)

wim said:


> I believe that's a DIN 7756 Vg5 thread. Not sure right now how to bring that across to U.S. or ISO standards, but a search on DIN 7756 (German Standards Institute) Vg5 (Vg = Ventilgewinde > valve thread) might get you the information on the tap you need. Also try "Sclaverand" in your search, which is another name for "Presta" [valves]. FWIW, here are the details on DIN 7756 valve threads.
> http://www.gewinde-normen.de/en/valve-thread.html


By that table, it'd be M5 x .7, which is decidedly non-standard. 

Not sure we're gonna solve this one.


----------



## martinrjensen (Sep 23, 2007)

*replace the tube?*

You are talking about a $7.00 tube here. Are you trying to repair some damage or modifying something.


----------



## wim (Feb 28, 2005)

danl1 said:


> By that table, it'd be M5 x .7, which is decidedly non-standard.
> 
> Not sure we're gonna solve this one.


Agree—and it would help if the German bicycle and automobile valve repair tool manufacturer would specify the thread on the tool he advertises....


----------



## restart (Aug 11, 2004)

Ahhh, interesting. My dial caliper shows an OD of just over 4.65 mm at the threaded area and I had a hard time even getting a 5 mm tap to enter the hole. 5 mm sounds too large. Next step: hit the machine shop at school and see what we can determine with better tools (and a better operator than me). That will be on Friday. I'll keep everyone posted.
Thanks for all the input
Mike


----------



## restart (Aug 11, 2004)

Martin, it's a brand new tubular tire, the tapping adventure will be a LOT easier than trying to replace the tube and sew up the tire again.


----------



## restart (Aug 11, 2004)

well heck I'd buy the tool if I could get one


----------



## jmlapoint (Sep 4, 2008)

Why not take an old Presta Valve and cut it open longitudinally and measure the threads directly. I did this once with an Air Cut-Off Tool; curious to see what the inside of a Presta Valve with removable Core looked like.


----------



## restart (Aug 11, 2004)

John, yes, that is the current course of action. I have to get a metric thread gauge; should be able to do that tomorrow. Will keep you posted.


----------



## restart (Aug 11, 2004)

OK - here's what I learned at the machine shop at school. The closest metric thread we can get is 5mm diameter with .6mm pitch. Definitely nonstandard, no one of our sources lists such a tap. However, this is VERY close to the SAE 10-40 size which is also a little unusual being a US Extra Fine thread. Bottom line: I tapped the hole with the 10-40 tap and the adapters thread on pretty well. A little tight, but it is a practical solution. I hope this can help others with similar issues.


----------



## SickBoy (Oct 29, 2004)

I have some Ritchey tubulars that I got pretty cheap ($20/ea). I want to mount them to some carbon wheels but I HATE, repeat HATE the 'normal' Zipp-style valve extenders because I always have issues with the valve nut not accepting air or the extender leaking. And, of course, whenever this happens you have to peel off and reglue the tire to fix it. I much prefer the Tufo-style extenders that you remove the valve core and screw in there. Trouble is, these tubulars don't have removable cores. So - using the info from above, I'd like to cut the valves off the top of these tires, tap the shaft (that's what she said) and screw in the extenders.

restart, what did you use to cut your valve shafts? I assume I am going to want to be careful not to bend or misshape the valve shaft, so maybe a fine-threaded hacksaw?


----------



## Bike Poor (Sep 17, 2009)

SickBoy said:


> restart, what did you use to cut your valve shafts? I assume I am going to want to be careful not to bend or misshape the valve shaft, so maybe a fine-threaded hacksaw?



I would use a dremel with a cut off wheel.


----------



## restart (Aug 11, 2004)

I used a small tubing cutter (like the plumber's tool). With a little patience it worked great and cut perfectly square. Somewhat longer term report: tires hold air just fine.


----------



## martinrjensen (Sep 23, 2007)

Machine shops should have a thread gauge that will allow you to figure out what the threads are. It may be metric.


----------



## restart (Aug 11, 2004)

Martin, yes, see previous entries on the thread, we have gone the metric thread gauge route.


----------



## JSB Tech (May 31, 2021)

restart said:


> I'm looking for the thread spec on the part of the Presta valve that screws into the valve stem. Basically I need to tap a short stem to fit an extender on it so I can continue to use the tubular tire. Thanks for any relevant info.
> Mike


I found that a piece of either Teflon or Nylon 5/16" tubing would work. Drill out the tubing to a no.1 drill or just under 1/4" cut to about 3/4 to 1" and thread it on. I found a papermate pen worked great but the plastic didn't hold up for more than one use before splitting. The nylon or Teflon should resolve that and it did.


----------



## Kerry Irons (Feb 25, 2002)

JSB Tech said:


> I found that a piece of either Teflon or Nylon 5/16" tubing would work. Drill out the tubing to a no.1 drill or just under 1/4" cut to about 3/4 to 1" and thread it on. I found a papermate pen worked great but the plastic didn't hold up for more than one use before splitting. The nylon or Teflon should resolve that and it did.


Impressive. Reviving a thread from 17 years ago. I'm sure these folks have been watching closely for a solution for all these years.


----------



## cmh (Oct 5, 2002)

Came here looking for this exact info, old thread or not.



Kerry Irons said:


> Reviving a thread from 17 years ago


Math wasn't your strong suit in school, was it?


----------

