[Newbie] Help with Finding and Using Thread-Pitch Gauges

J

JDavis

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Hey guys,

So I’m trying to find a decent thread pitch gauge set, which I can use with in tandem with my digital calipers in order to identify the threads of most screws, bolts, and pipe threads that I come across; however, this has proven to be difficult.

I bought a set off of Amazon for $23 (see images 1 and 2), but it didn’t come with a reference guide or instructions of any kind, so I scoured the Internet looking for instruction and a proper reference guide, but I've come up a bit short.

Here is what I've learned:

The most common standards for Britain are Whitworth and BSF. American sizes are typically UNF and UNC. International sizes are typically Metric ISO Fine and Metric ISO Coarse. Whitworth, BSF, UNF, and UNC identify threads by threads per inch (TPI) and Metric uses the distance between two consecutive threads as the pitch. Apparently, there are both tapered and parallel threads for these systems.​

My questions:

Is my set any good, if not, where can I find a good set for under $100?

How do you use those three single-piece gauges that look like a more arrow dynamic version of the USS Enterprise? Are they used to check gap angles between threads as well as something else?

Where do I find a good reference manual and/or guide to use with my pitch gauges? I found a guide at CarBuilderSolutions.com (see 3rd image), however, it is pretty pixelated and doesn't seem complete.

My apologies for the length.

I'd appreciate any help that can be given.

Thank you,
-Jeff


gauges1.jpggauges2.jpgCarBuilderSolutions - Tapping Drill Sizes.jpg
 
I have no idea how accurate those gauges are but I suspect they will work fine. I use Starrett gauges because I trust them.

The arrow-looking things are known as fishtail gauges and are used to grind an accurate geometry on a threading tool. Of course, Imperial threads use the 60 deg gauge and the Whitworth uses the 55 deg gauge.

There are thread charts galore all over the net. The key bit of info you need to identify a screw is the OD of the shank of the screw. You then find the closest major diameter to your screw in a chart. That will usually tell you if it is Imperial or Metric and which tpi or thread pitches you should consider. Then you use your thread or pitch gauges to confirm which thread you have and you've identified your thread.

As an aside, Whitworth threads are not commonly used in modern metric fasteners; those are commonly 60 deg threads. Whitworth threads are still found in older equipment but are not nearly as common as the Metric ones.
 
The thing that looks like an arrow is a fish tail. It is used to set your threading tool properly in the lathe, and also serves as a gage when grinding your own tooling.
I'm a firm believer in buy once, cry once, so I always used Starrett gages. Not sure what they cost anymore since I've had mine for 30+ years.
As far as using the pitch gages. you keep trying one of the gages on the thread your checking until one fits in the thread properly. If it's wrong, it won't fit or it may rock.
Depending what you're getting into, you should be able to get by with just American and metric
 
Shoot me a private message if you need any of the above " objects " . Time for me to clear off the Foosball table ! :big grin:
 
The pitch gauges are simple to use. Just find the one which exactly fits the threads of your unknown thread. Drop one of the points in a thread valley and rock the gauge to fit in the remaining threads. If the the gauge points are coming closer to the start thread, the gauge is too fine aitch. If they are further away, the pitch is too coarse. If none seem to fit exactly, try switching from Imperial to metric or vice versa.

A measurement of the thread diameter with a caliper or micrometer will usually read slightly less than the nominal diameter. With these two numbers, you will have identify the thread.

The fishtail gauges are used as described above.
 
Is my set any good? Good for what?

I can't say it's not worth $23, but I can say that I'd rather have Starrett, Brown and Sharpe or Lufkin brand tools. Quality brand name tools come up on eBay for reasonable prices if you shop around and use good judgement (developed with experience). Sometimes they need considerable clean-up. A new Starrett 472 (51 threads) retails for about $80.

One difference between cheap models and quality models is the accuracy of the pitch. Many metric pitches are very close to TPI pitches. With a quality brand tool, I have more confidence that the tool is more accurate so those small differences in pitch are easier to distinguish.

Another difference is the crispness of the edges. I have seen inexpensive thread gages that have considerably "rolled" edges (as punched) that seem more difficult to read against a thread. On quality brand name tools, the leaves tend to be flatter right out to the edge and are easier to read.

The three center gages are primarily used to check the form of a cutting tool when grinding. Notice the edges of the center gages have TPI or mm scales.

The last image is a tap drill chart for many common size threads. They are common and all over the internet. Search "(inch, BSP, NPT, ISO, metric) tap drill chart" and take your pick.
 
There are way too many thread forms. Japanese metric has some variations from European metric. European metric uses British pipe/tube threads in either straight or tapered. Some Imperial threads are really close to metric. There are lots of "special" threads that luckily you only find on very specific items. Buy a good wall chart that lists most of the threads, their tap drill and their clearance drill. My chart has drill sizes listed in size order: fraction, metric, letter and number. Get a good 115 pc. set ($250+) of bits and it will cover most drill sizes even close enough to most metric. I have a set of metric but they are by too big of jumps. For 1/2 to 1" I've got a set (Silver & Deming) from Grizzly that are actually pretty good. For most things my go to are screw machine bits in cobalt. I have a few carbide bits for drilling out broken bolts and taps. I have a few left hand bits that work well for drilling out broken bolts. Usually they will just back the bolt out. Much better than easyouts. As you can tell this is part of the rabbit hole phenomenon.
 
You've got way more than I and I get by just fine. I don't know why there are 5 different fanouts. I have one like this
The only use (at least for my eyes) for the fanout pieces is to determine how many treads per inch (non metric) or how far between threads (metric). At least my eyes would have trouble determining between 55* and 60* in such a small sample.

Use what you have and if you find you don't like it SPEND MORE MONEY!
Aaron

By the way. Welcome to the site!
 
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