# Digital Calipers & Pitch Guages



## jch79 (Dec 2, 2006)

Hey all!

I'm interested in picking up a pair of Digital Calipers & a thread guage.

(1) First, digital calipers:

-Brands considered: Mitutoyo, Brown & Sharpe, or Starrett. I like that Starrett is Made in USA, so I'm leaning toward them. (I don't think Mitutoyo or B&S are made in USA?)

-It would be for light-duty use - I don't need super-heavy duty tools, but I like to own quality tools.

-Size: 6 or 8 inches. Since I like smaller lights, I think 6" would probably work.

-Digital is preferred, but is it THAT much more accurate?

-Price limit... well, I don't want to bust my bank account, but it's not super important.


(2) The a thread guage:

-I haven't found a lot of info on these, but it seems they're expensive and somewhat complicated.

-Preferred, again Made in USA.


Anyways, if you guys would share your thoughts, as well as Model Numbers and Where to get (websites), that would be awesome.

Thanks a lot! 

john


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## cy (Dec 2, 2006)

I've got a Starrett 6in digital calipers in excellent condition available. 
reason for selling is I've got 5 pairs and Starrett is not getting used.

available for $100 shipped conus.... please PM if interested...
these are the good USA made version. 

6in calipers is size you want...



jch79 said:


> Hey all!
> 
> I'm interested in picking up a pair of Digital Calipers & a thread guage.
> 
> ...


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## jch79 (Dec 2, 2006)

PM on its way cy! Color me interested!


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## CNC Dan (Dec 2, 2006)

jch79 said:


> -Digital is preferred, but is it THAT much more accurate?



No, not more accurate, but more usefull. You can set the origin (0.000) at any point, and then measure diferances. Like if you wanted to make several parts all the same size. You would make one part to the required length, and set the calipers to zero on that part, then measure other workpieces. The measurment will be how much you need to remove to make that part match.



jch79 said:


> (2) The a thread guage:
> 
> -I haven't found a lot of info on these, but it seems they're expensive and somewhat complicated.



What kind of thread guage. There are several.

I would recomend pitch micrometers to measure pitch diameter, and pitch guages to measure the TPI of a thread you want to match.


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## cy (Dec 2, 2006)

...


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## wquiles (Dec 2, 2006)

I have a really nice Fowler IP-54 Digital caliper (splash proof), but 9 out of 10 times I use my Mitutoyo 6" Dial caliper (0.100 per revolution), with IN/OUT carbide tipped jaws, and TiN-coated sliding surfaces for little/no wear. It is simply AWESOME and spot on. This would be the last caliper you will ever need. I still regret buying the cheaper calipers I had before I finally got this one 

Will


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## Rothrandir (Dec 3, 2006)

For dial calipers, Brown and Sharpe makes the best (along with Tesa and Etalon, which are all essentially the same). Ironically, the B&S calipers can often be found for about $80...the cheapest you are likely to find for a quality set of calipers (fowler, chinese, etc etc etc not included)

For digital calipers, Mitutoyo is considered the best.

As a side question, are Starett calipers really still made in the US? I know a lot of their products are not...
Also it should be noted that Starett uses softer metal in their calipers than other brands, which makes them more subject to bending and other injury...

I've got a pair of 6inch B&S dial calipers, and an 8inch pair of Mitutoyo ip-66 rated calipers.
I used to use the Browns at work, but decided to take them home to use in the home shop (where I had been using cheap chinese calipers), and buy the 8inchers for work, since I never need more than 6inches at home, and often at work I will need up to 8inches. Also the ip rating means that the mitutoyos are coolant and dustproof (to a degree)...important when you're working in a machine shop where you constantly face both these issues...

As far as accuracy and feel, I prefer the Browns. I also prefer a dial over digital.


For thread measuring, there are several options.
The cheapest is to buy a set of thread pins. These pins come in a set of various diameters (3 pins per size). And are placed in the pitch of the thread opposite each other (2 on one side, 1 on the other), and you measure across them with a micrometer. Subtract the constant listed on the chart, and that is your thread pitch.
(these can be a pita to use. A good choice if you don't require them often and aren't looking to spend a lot, but are more time consuming and potentially frustrating than other methods.)

There are also thread micrometers, which work the same as a regular micrometer, but are obviously for measuring threads..

Then there are after market tips to go on micrometers. These are the most versatile as you can place them on different sized micrometers to read multiple diameters. These will come with a magic number (the length of the tips), that you subtract from the number you reach.
However, to be most effective with these, it may be required that you buy additional micrometers (if you don't have them), Since thread sizes on the large end may require you to move to a larger mic. (For instance, if measuring a 7/8 thread, you will need to use a 1-2 mic rather than a 0-1 mic, because the anvils take up several hundred thou (.450 for the set I use)


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## cy (Dec 3, 2006)

starrett caliper offered above is model 721 which are USA made. 
newer models like 799 global series and not made in US. 

most used was a set of brown & sharpe dial calipers my dad gave me. but being able to switch from MM to SAE and being easier to read switched me to mitutoyo digital calipers. 

personal preferences decides what I actually use. since I've not used these in production. no clue about wear/hardness resistance. 

as pointed out, for precision work you'd pull out micrometers anyways. calipers gets me close enough for most jobs and are pretty darn handy!



Rothrandir said:


> For digital calipers, Mitutoyo is considered the best.
> 
> As a side question, are Starett calipers really still made in the US? I know a lot of their products are not...


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## jch79 (Dec 3, 2006)

Wow... thanks for the responses guys!  It seems like you can't really go wrong with Mitutoyos or Starrett. So far the Starrett 721 like cy mentioned, or the 797B (which is made in the USA) are my top choices.

As for the thread guages - it seems like something called the three wire system is the best way to go, however it looks like you need several tools to do so? 

john


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## TranquillityBase (Dec 3, 2006)

John, are you looking for something to measure actual thread pitch, or a gauge set to determine tpi?

The three wire is for measuring actual thread pitch, and a thread pitch leaf gauge set is for tpi indentification...The names of the tools make this confusing.

TB


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## will (Dec 3, 2006)

TranquillityBase said:


> John, are you looking for something to measure actual thread pitch, or a gauge set to determine tpi?
> 
> The three wire is for measuring actual thread pitch, and a thread pitch leaf gauge set is for tpi indentification...The names of the tools make this confusing.
> 
> TB



Is the three wire set used to measure thread depth, thread pitch, or threads per inch (TPI)

thread depth - how deep the threads are 
thread pitch - the angle of the cutting tool, most threads are 60 degrees
threads per inch - how many threads are in a one inch segment. 

I always thought the three wire set was used just to measure the depth of the thread.


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## jch79 (Dec 3, 2006)

Geez! Now I don't know what I'm looking for! I was looking to measure a current light that I have, and then give the measurements to someone to use to base a new light off of - so I suppose I need to measure depth, pitch, and tpi! Hmph.
john


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## will (Dec 3, 2006)

Threading is stated as diameter by threads per inch ( or the metric equivilant ) 

for example 1/4 x 20 would be a 1/4 inch outside diameter with 20 threads per inch. The outside diameter is almost always a little smaller that the stated size. Measuring an inside diameter is from the bottom of the thread. This is usually done with a thread guage for that particular diameter and tpi. 

Cut to the chase - if you have a well known brand of light - someone in the CPF community will probably know what the threading is for that light.


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## TranquillityBase (Dec 3, 2006)

will said:


> Is the three wire set used to measure thread depth, thread pitch, or threads per inch (TPI)
> 
> thread depth - how deep the threads are
> thread pitch - the angle of the cutting tool, most threads are 60 degrees
> ...


 
You're correct...Three wire method is for measuring thread pitch diameter.

I think John is looking for *screw/thread pitch gage set *which is a visual reference for determining tpi. Screw/thread pitch and tpi are one in the same, *thread pitch diameter* is the true measure of the thread depth.

TB


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## jch79 (Dec 3, 2006)

will said:


> Cut to the chase - if you have a well known brand of light - someone in the CPF community will probably know what the threading is for that light.


 You got me!
As I don't have any experience in flashlight design or mechanics, I'm basing a flashlight idea off of a current light, however I'd rather not just out and ask for measurements (yet!) - learning is half the fun here... at least I hope it will be!  :thinking: :shrug:


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## jch79 (Dec 3, 2006)

TranquillityBase said:


> You're correct...Three wire method is for measuring thread pitch diameter.
> 
> I think John is looking for *screw/thread pitch gage set *which is a visual reference for determining tpi. Screw/thread pitch and tpi are one in the same, *thread pitch diameter* is the true measure of the thread depth.


Thanks Scott & Will for clarifying a little more. But if I'm looking to give specs to someone, shouldn't I have to know TPI & thread depth? Thus, I'd need two tools, correct?
Getting there...  
john


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## will (Dec 3, 2006)

jch79 said:


> You got me!
> As I don't have any experience in flashlight design or mechanics, I'm basing a flashlight idea off of a current light, however I'd rather not just out and ask for measurements (yet!) - learning is half the fun here... at least I hope it will be!  :thinking: :shrug:



That's how I learned a lot of stuff. If you have a complete light, get a caliper and measure the outside diameter of the threaded part, go right on top of the threads, important, use a light touch when measuring. That will give you the outside diameter, For example 1/4" x 20 will read something like .240 on the caliper, the very tops of the threads are almost always rounded a bit. The next thing you need to know isthe threads per inch (tpi) or threads per MM - I am not a metric person and I could be wrong about that. 
There are TPI guages out there to help with that. You can also set the caliper to one inch and count the number of threads in that space. 

almost all threading is done with a 60 degree pitch, but there are exceptions. some threading is done with a rounded tool instead of a point, also some threading has multiple start points. A mini-maglite has 4 startpoints on the threading on the head. 

best of luck to you..


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## jch79 (Dec 3, 2006)

Good stuff... thanks Will! Man I love CPF.


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## PEU (Dec 3, 2006)

A digital caliper (chinese) and a thread gage is all I use for thread measurements, having these is cheap and solves most of the problems of a flashlight modder, if you need to go professional, then consider the better brands commented in this thread 


Pablo


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## gadget_lover (Dec 4, 2006)

There are standards for most threads. A 20 tpi thread should always be the same depth, regardless of the diameter of the piece. What causes problems is that there is no law that requires a 20 tpi part to follow that standard. They can be cut deeper, shallower, etc. In practice, you can't deviate too far when using a 60 degree tool without messing up the thread profile.

Daniel


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## Anglepoise (Dec 4, 2006)

John,
Excellent advise ^^^^. I would only add a couple of comments on design that might help.

It is important to decide right away if the light design will be 'stand alone' or if you will be mixing and matching components from another maker. 

The Aleph system would be an example of the later. 

Now a designer building a custom, might decide to use 24 or 32 TPI for convenience. Both these TPI's are a multiple of most American lead screws so it simplifies threading. 

However it would be no use if the battery tube ( example ) was required to mate with another light with 20 TPI treads. The outside diameters can be the same in both instances, but they will not thread together.

As was mentioned above, there are different classes of fit and if a custom light must mate with something else,then send the example of the 'something else' to the machinist so everything fits.


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## jch79 (Dec 4, 2006)

I'm a-tryin' to do a custom, so it's not that important that it matches with anything else; I'm just trying to get an idea of what a few of my lights are as far as threading.

The design won't be Aleph-compatible oo:, so matching threading with another light isn't important - I just want to better understand how different-sized threading affects the feel of turning a head or tail in your hand.

Thanks!
john


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## Anglepoise (Dec 4, 2006)

These cost around $20.00 and are available in SAE and Metric.
Quickly tells you the TPI of any thread.


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## jch79 (Dec 4, 2006)

Thanks Anglepoise! I saw that tool somehere on the web, and didn't understand exactly how it worked... now, after looking at it for more than two seconds, it makes perfect sense, (duh) and 
john


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