# Need help figuring out a square thread pitch



## ARC-170 (Feb 14, 2022)

I have an old Milwaukee vise from the 70's, I think. It was made in Japan. It needs a new screw. Material was free. However, I can't seem to figure out the thread pitch. It appears to be a 5/8-6, but there only seem to be a little more than 5 threads in an inch. It could be metric, since it measures 0.629" (16mm is 0.6299") in diameter. I could not find a thread chart for square, metric threads.

The threads themselves (let's call these the "male" part) are 0.108" wide and the grooves (the "female" part) are 0.116" wide. The thread pitch would then be 0.224" [5.69 mm]. I measured this at the ends where I thought there would be less wear. If this is a 5/8-6, then the pitch would be 0.166, right (1/6=0.166)?

I've included a picture. It's 7/8" between corresponding points on the thread (4" to 3-1/8" in the photo). I even checked a 1/4-20 and counted 21 threads, so I'm sure I'm missing something.


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## mickri (Feb 14, 2022)

Have you checked Mr Pete's videos?  I think that he has a video on cutting square threads.  I'll also check my old machinery handbook to see what it has to say about square threads and report back.


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## mickri (Feb 14, 2022)

The MH didn't have much to say about square threads other than they are difficult to machine.  The numbers that you posted indicate a thread just under 5 tpi according to the chart in the MH.  Sorry I couldn't be of much help.


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## ARC-170 (Feb 15, 2022)

Thanks, Chuck! (@mickri)

I think I figured it out. It's a 5/8-4.5. I counted 9 threads (male and female) in 2 inches and 18 in 4 inches. I also took a look at my lathe and noticed it can cut 4, 4.5, 5, and 5.75 threads per inch. It just didn't occur to me that there could be anything other than whole numbers!

I also found a chart that has thread depths and pitches for square threads and the numbers closely match my measurements.


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## Alcap (Feb 15, 2022)

Would you mind posting a link to the square thread chart you found ?


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## IamNotImportant (Feb 15, 2022)




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## RJSakowski (Feb 15, 2022)

If determining thread pitch by counting the number of threads in an interval, use the largest intreval possible for best accuracy.  One could assume some nice neat number for the pitch but that could be a mistake, especially when dealing with both inch and metric threads.


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## ARC-170 (Feb 15, 2022)

Here's the chart I used:


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## MrWhoopee (Feb 15, 2022)

Does is bother anyone else that the OD is .629 (16mm)?


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## ARC-170 (Feb 15, 2022)

MrWhoopee said:


> Does is bother anyone else that the OD is .629 (16mm)?


It bothers me, too, actually. The thread pitch on metric threads is measured between 2 corresponding points on the thread. I measure 2.62mm and 2.92mm for the "male" and "female" parts for a total of 5.54mm. I wonder if this could be a 16x5.5.

But, I couldn't find any reference for metric square threads. I found plenty of metric thread references, but nothing specifically addressing metric square threads.

The fact that the pitch was exactly 9 teeth in 2 inches and 18 in 4, along with the teeth dimensions being within wear tolerances of the dimensions in the table leads me to thinking this must be an inch thread. I used calipers to measure the diameter and they could be off a thousandth or two.


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## extropic (Feb 15, 2022)

Just to muddy the waters a little more:

5.5 TPI = .18182" pitch

4.6mm pitch = .18110" pitch

Very hard to tell apart when measuring a worn part in a hobbyist environment.

Measure very carefully.


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## Illinoyance (Feb 16, 2022)

To measure pitch I use a regular pitch gauge for V threads. 
I disagree with the person that saids square threads are difficult to cut.


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## ARC-170 (Feb 16, 2022)

extropic said:


> Just to muddy the waters a little more:
> 
> 5.5 TPI = .18182" pitch
> 
> ...


Is 4.6mm a standard metric thread pitch?


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## extropic (Feb 17, 2022)

ARC-170 said:


> Is 4.6mm a standard metric thread pitch?


I don't know.
However, .629" diameter is a lot closer to 16mm than to 5/8".
It makes sense to me that a metric pitch would be used on a metric diameter.
Not a certainty. Perhaps only mudding the waters.

If your lathe can cut only TPI, then cut a 5.5 TPI sample, long enough to have full length engagement with the nut, and try it.

If your lathe can cut either TPI or mm pitches, sample and try both.

Coating the sample screw threads with Dykem blue might help show contact where it's rubbed off.

To be certain everything is Kosher, buy a custom tap, say .635-5.5, and cut a 5.5 TPI screw to fit. That approach might push the project out of an acceptable budget. YMMV.

By the way, you have called it a "Square" thread form. I certainly can't tell from the photos but you need to be absolutely certain of the included angle between adjacent thread flanks (0° for a true Square thread form).

Good luck.


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## jmkasunich (Feb 17, 2022)

I think it might be 6mm metric pitch.
At 6mm, one thread would be 0.236", just under 1/4".
2 threads = 12mm = 0.472" = 7 and a half sixteenths of an inch
3 threads = 18mm = 0.709" = 11 and 1/3 sixteenths
4 threads = 24mm = 0.945" = just a hair over 15 sixteenths
5 threads = 30mm = 1.181" = not quite 1 and 3/16
6 threads = 36mm = 1.417" = half a sixteenth more than 1-3/8

Compare those measurements with the 1 thru 6 markings below:




For better accuracy measure over the longest possible distance.  And remember - you don't count the first thread crest!
Put one jaw of your calipers on the left side of a thread crest.  Visually align the other jaw over the* 21st* thread crest to measure *20* thread pitches.  Then divide by 20, convert to mm, and see whether the inch or mm number makes more sense.


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## Jake M (Feb 19, 2022)

ARC-170 said:


> The threads themselves (let's call these the "male" part) are 0.108" wide and the grooves (the "female" part) are 0.116" wide. The thread pitch would then be 0.224" [5.69 mm]. I measured this at the ends where I thought there would be less wear. If this is a 5/8-6, then the pitch would be 0.166, right (1/6=0.166)?
> 
> I've included a picture. It's 7/8" between corresponding points on the thread (4" to 3-1/8" in the photo). I even checked a 1/4-20 and counted 21 threads, so I'm sure I'm missing something.




You're looking at something that came from a country where the readily available tooling would be metric, for an imperial brand name, with a history or custom of using imperial measurements.   If I had to guess if it was imperial or metric, or a close approximation of either one,  I wouldn't.  It's not an interchangeable piece with anything except that model of vise (and perhaps a couple of others in the same catalog), so ti need not be a standard at all...   You've got a diameter that screams metric, but pitch that cries imperial.  And everything's worn.  Probably not evenly.  Add to that, leadscrews on non-precision mechanisms tend to be far from accurate in dimensions, far from consistant from one end to another, and tend to have big liberties taken with their thread forms.  And loose tolerances to make absolutely sure that the biggest screw they ever make will still wiggle around a lot in the smallest nut they ever make.  And they need that "slop", as vises have slop by design, you really don't want a precision fit  thread and nut anyhow.

Suggestion-  Place the vice screw in your lathe.  Don't worry about being too precise, if it looks straight(ish), it's straight enough for this.  Set up the 4-1/2 thread pitch which this might be, and that you can cut...  Mount a pointer, a nail, a pencil, anything pointy that will fit in your favorite tool holder, line it up, and (by hand), turn the chuck (Or turn it by the leadscrew handle if that needs resetting every half a turn to clear the lathe anyhow...) to let the threading mechanism in the lathe trace the corner of a thread thread from one end to the other.  Then you'll know without any doubt if you can replicate this screw.


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## ARC-170 (Feb 23, 2022)

jmkasunich said:


> I think it might be 6mm metric pitch.
> At 6mm, one thread would be 0.236", just under 1/4".
> 2 threads = 12mm = 0.472" = 7 and a half sixteenths of an inch
> 3 threads = 18mm = 0.709" = 11 and 1/3 sixteenths
> ...


I get 113.4mm or 4.467".

METRIC:
113.4/20=5.67mm thread pitch, if there is such a thing. It seems most metric threads are either X.0, X.25, X.50 or X.75. For this to be 5.75, the distance for 20 threads would be 115, for 5.50 it would be 110.

INCH:
4.467/20=0.223, 1/.223+ 4.48 TPI. Real close to 4.5 TPI (0.2222). The length would be 4.444 to be exactly 4.5TPI.  My measuring could be off a tad, since I was eyeballing where the right caliper was measuring to.

This might be one of those threads that's close to both an inch AND metric one.


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## ARC-170 (Feb 23, 2022)

Jake M said:


> You're looking at something that came from a country where the readily available tooling would be metric, for an imperial brand name, with a history or custom of using imperial measurements.   If I had to guess if it was imperial or metric, or a close approximation of either one,  I wouldn't.  It's not an interchangeable piece with anything except that model of vise (and perhaps a couple of others in the same catalog), so ti need not be a standard at all...   You've got a diameter that screams metric, but pitch that cries imperial.  And everything's worn.  Probably not evenly.  Add to that, leadscrews on non-precision mechanisms tend to be far from accurate in dimensions, far from consistant from one end to another, and tend to have big liberties taken with their thread forms.  And loose tolerances to make absolutely sure that the biggest screw they ever make will still wiggle around a lot in the smallest nut they ever make.  And they need that "slop", as vises have slop by design, you really don't want a precision fit  thread and nut anyhow.
> 
> Suggestion-  Place the vice screw in your lathe.  Don't worry about being too precise, if it looks straight(ish), it's straight enough for this.  Set up the 4-1/2 thread pitch which this might be, and that you can cut...  Mount a pointer, a nail, a pencil, anything pointy that will fit in your favorite tool holder, line it up, and (by hand), turn the chuck (Or turn it by the leadscrew handle if that needs resetting every half a turn to clear the lathe anyhow...) to let the threading mechanism in the lathe trace the corner of a thread thread from one end to the other.  Then you'll know without any doubt if you can replicate this screw.


I thought the same as you. The chart I found leads me to believe this is an inch thread, but I will have to try your suggestions and see what I come up with.


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## Illinoyance (Feb 23, 2022)

Thread it 4.5 tpi. The nut is too short to notice the difference.  Just make sure the thread with and land width match the original.


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## ARC-170 (May 1, 2022)

I finished the screw. To my surprise and delight, it actually works! It was a 5/8-4.5 thread, but the thread depth was about 0.072", not the 0.111" called for on the chart I posted.









I had to make a new handle, since I didn't really want to cut the old one and have to make a matching cap.

My vise now goes together smooth. The only items I had to buy were 7/16" rod for the handle, the rubber washers and a bigger e-clip. I made the shaft a bit bigger so it fit inside the vise body tighter so I needed a bigger diameter retaining clip. I used scrap for everything else.

Thanks for the help!


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