# Standard thread sizes?



## euroken (Feb 12, 2009)

Hello hello! Hope one of you experts can help a rookie out 

I took a caliper in an attempt to figure out the thread pitch for one of the Nitecore lights.

I had to calculate the thread per inch number since the threaded portion was less than 1/4", so had to count the threads and extrapolate the per inch value.

I measured something like this:

in inches:
major diameter = 0.684" (I assume 11/16")
threads per inch = 0.096" in three peaks, which equates to 31.25 tpi

in mm:
major diameter = 17.4mm
pitch = 2.45mm in three peaks, which equates to 0.817mm in one turn

Do these numbers match any standard thread sizes? When I searched the web, I found 11/16" major diameters but it only had 11 tpi. I couldn't match the metric number to any charts that I've seen on line.

Can anyone shed some light? No pun intended


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## precisionworks (Feb 12, 2009)

For under $20, you can buy both a Metric & a SAE thread form gage (also called a screw pitch gage).












Those are both Starretts, but most of the others work just as well and cost less.


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## gadget_lover (Feb 12, 2009)

Manufacturers don't have to use any particular thread. All they need is for their parts to match.

Any thread can be used on any size part. The choice depends on how many turns you want to use to open the part as well as how deep the threads can be.

Are you looking for a tap to match it?

Daniel


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## BoarHunter (Feb 13, 2009)

I am a bit suprised by your measures as common fine pitch used for tubing are 1, 1.25 and 1.5 in the diam range of 10 to 30.

I just bought recently a Nightcore Defender Infinity and beeing curious, I too measured the threads as I may envision to build an extender tube for it.

I was suprised to see that the head and tail are different diameters ! Most probably to avoid incorrect assembly.

As for being standard, they don't seem to be except the tail that fit a M18X1.25 but definitely not the head which is closer to 19.
They are quite loose too.

It seems that they try to use common pitch to reduce cutting tools inventory but choose the nominal diam. that suits their needs instead of sticking to international standard. With CNC this is no big deal as I doubt they rely on standard tap and die.
There is no reason to use gaz pipe thread either or exotic pitches.


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## euroken (Feb 13, 2009)

Thank you all for your replies!

I have never machined or plan on machining in the near future since I just don't have the knowledge or the access to equipments and such. I wanted to modify the retaining ring on the Nitecore Extreme switch since I hate having to use a tweezer to unscrew it (thought just an awkward design, especially when the clicky on these lights are prone to problems based on what I've read so far). That being said, I'm hoping to machine another retaining ring that will have to match the thread diameter and pitch of the female thread of the light's tailend.

I found a site where I can draw up the part in 3D, using one of their downloadable programs and I can upload it for their review and pricing of the part. I have the drawing complete except for the thread size. I know, this sounds quite amature-ish, but that's exactly what I am when it comes to 'machining.' 

-precisionworks- Thank you for the suggestion, and thought that would be my next option but now I'm not so sure anymore. Sounds like the gages will just be a paper weight to me if the threads are not standard.

-gadget_lover- Haha, I have nooo idea what you mean when you say "tap" to match it  But sounds like, yes. I'm trying to match the existing threads so that the new part won't damage the main threads on the light's body.

-BoarHunter- Does 31.25 close to a common pitch? I saw somewhere on the internet that camera lens equipments have common pitch of 24, 30, and 32. 

I'm pretty comfortable with the thread diameter since I was able to accurately measure the major diameter of the retaining ring. My biggest concern, obviously, is that the mismatching threads will damage the threads on the body. Nitecore doesn't sell spare parts by them selves like the Fenix.

Is there a better way of going about this to accurately match a thread on a existing part? 

Thank you all again for your help :thumbsup:


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## BoarHunter (Feb 13, 2009)

Sorry but I don't see what you mean by 31.5 ... the pitch is the distance between two peaks and by default is expressed in mm. For old equipment like water and gaz pipes, they used to express pitch in number of turn per "inch" (an ancient measure that had been defined as 25.4mm in the 19° century).

I doubt that Nitecore use this kind of "pitch", China is quite a modern country.

Note that if by 31.5 you mean turn per inch, in fact the pitch is most probably 0.75 which is very common too for very fine thread. I have a small Fenix and it is what I measured on it.


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## jhanko (Feb 13, 2009)

Thread pitch for the Nitecore D10 & EX10 is 1.25mm.

Jeff


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## euroken (Feb 13, 2009)

-BoarHunter- Yes, I meant 31.5 threads per inch and not "pitch". The pitch was 0.817mm from what I can tell.

-Jeff- Thanks for the info. From what I'm measuring, I'm not getting near that number. 

I do know that the head from Surefire E series will fit NEX body, which I believe is 13/16-20, from other postings, but unfortunately this information is of no use for me at the moment. 

Any other way to "accurately" determine or measure the thread size?


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## gadget_lover (Feb 13, 2009)

All of the accurate methods require tools of some sort.

You can use a stong magnifier/microscope and a precision scale to accurately measure the exact distance from the center of one thread peak to the center of the next. A little math will then give you TPI (threads per inch) for imperial threads) or pitch for metric threads.

A thread guage is a simple little device the size of your finger with sample threads on little metal strips. Less than $10 at the hardware store. You simply try each one till it matches exactly.

BTW, a "tap" is the device used to cut threads in a hole so that you can screw something into the hole. They come in standard sizes in bot metric and imperial threads. A "die" is used to cut threads on the outside of a tube or bar.

Good luck with your endeavor. Cahnces are that you will need to send your tailcap to someone so they can make a matching part for you. It's easier to make a wrench that fits the holes. 

Dan


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## precisionworks (Feb 13, 2009)

> All of the accurate methods require tools of some sort.


+1

An optical comparator, with grid calibrated in threads/inch or threads/mm, is the easiest & most precise way. Most factories that make threaded products have one or two in the QC Lab, and might measure your light if you ask the right person to do that. They're a little pricey, starting around $20k, and I've never seen one in a home shop






Less expensive is a thread micrometer, which has V shaped anvils that fit all the way down to the root of the threads. Under $500 for a multi-anvil set:







Lots of machinists use thread measuring wires, which are easy to use if you can stand on your head & sing at the same time. If you can't stand on your head, you'll need a micrometer stand which frees both hands to position the wires. About $25 for the wires + $25 for the stand:







Last in line is the lowly thread form gage (my previous post) which is a bargain at $10.


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## euroken (Feb 13, 2009)

Thank you Dan and Precisionworks!

I didn't realize things could get a little complicated. I feel like I'm being initiated into the world of modding.

Well, let me see if I can stop by the local machine shop (once I find one) and see if I can squeeze some information from them.

Thank you all again for your insight!


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## Torque1st (Feb 13, 2009)

euroken said:


> Any other way to "accurately" determine or measure the thread size?


Use the thread pitch gauges mentioned by user precisionworks then an accurate set of thread micrometers or thread wires to get the pitch diameter. Just measuring the outside diameter of a thread is not accurate because a standard threadform is truncated.

BTW, I have seen an optical comparator in a home shop... Lucky guy!


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## euroken (Feb 14, 2009)

Torque1st said:


> BTW, I have seen an optical comparator in a home shop... Lucky guy!


 
Optical what??? 

Thank you Torque1st. I'll update the post if I make some progress.


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## euroken (Feb 17, 2009)

I'm back! And with more questions!

Thought I was making some head way and then hit another wall.

I was able to get the actual thread spec from the manufacturer. The size was M17.5x0.8. But evidently, this isn't enough to get the thread machined properly. The machining company can set the major diameter to what I need but the minor diameter should also be defined. 

Evidently, based on United Thread Standards, the minor diameter of the thread for this size should be 16.53 mm. When I meausre the inner clear diameter of the female thread, I measure 17.2 mm. How can I be sure this will be correct?

Do I need to specify what standard the threads should be machined to? Getting a little dizzy with all this information :sick2:


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## gadget_lover (Feb 18, 2009)

The major diameter is the nominal diameter - 1/8 of the thread height. I figure the thread height as .69mm

17.5 - (1/8 * .69 * 2) is 17.3276, which matches close to your major diameter measurement.

Minor is major - 5/8 of the thread height....
I figure the minor diameter to be 17.3276 - (5/8 * .69 * 2) is  16.4652

Since you are measuring a larger bore than what I'm calculating, it simply means a looser fit. It seems that the fit would be very loose if the major is 17.4 and the minor is 17.2

Please do NOT trust my numbers unless someone confirms them, as I frequently transpose numbers.

The thread of the male part must be equal to or smaller than called for by the standard and the female part must be equal to or larger than the standard. This avoids the problem of having the threads bottom out.

Daniel


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## gadget_lover (Feb 18, 2009)

....more thoughts....

You have to specify the major and minor so that YOU take the blame if they do not fit. They have no access to every light that these will fit on. 

You do have to specify that it is ISO metric thread form.


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## euroken (Feb 18, 2009)

Thank you gadget_lover!

I guess I have to bite the bullet and see what happens!


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