# Measuring Large Small Holes



## RJSakowski (Feb 3, 2018)

When measuring the diameter of small holes, my favorite tool is a pin gage.  I have sets up to 1/2" but yesterday, I needed to measure a .903" hole.  Ideally, I would have a full set of pins to 1" but at somewhere near a $700 even for an import set, that's an expensive bunch of metrology.  I used a .500" pin and a .403" pin side by side to make the measurement.  It worked great.  A .500" + a.402" was loose, a 500" + a .404" was a no-go, and a .500" + a .403" was just snug.


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## Tozguy (Feb 3, 2018)

Typo on the no go?


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## RJSakowski (Feb 3, 2018)

Tozguy said:


> Typo on the no go?


Yes!  Thanks for catching.


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## Ray C (Feb 3, 2018)

RJ,

How about a telescoping gage?   Man, I love those things and get a lot of mileage out of them.


Ray


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## westsailpat (Feb 3, 2018)

Tri mic , they are expensive and limited range but nice .


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## benmychree (Feb 3, 2018)

Another choice is Brown & Sharpe tapered hole gages; one side is radiused, the other flat; they are used in pairs flat side to flat side and wedged into the hole with one end protruding from the hole and measured with a micrometer other options are small hole gages, telescoping gages and inside mikes. I also have a set of B&S flat plug gages, 3/8 to 2" by 1/16ths, good for detecting taper and fit in nominal size holes.


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## benmychree (Feb 3, 2018)

westsailpat said:


> Tri mic , they are expensive and limited range but nice .


The only Tri Mic (Made by B&S) that I am aware of is a OD micrometer with three contact surfaces and is used to detect 3 lobed out of roundness and diameters of 3 or 6 fluted of end mills; Is your post of something entirely different?


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## Tony Wells (Feb 3, 2018)

Intrimik I believe, John.


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## benmychree (Feb 3, 2018)

Tony Wells said:


> Intrimik I believe, John.





Tony Wells said:


> Intrimik I believe, John.


OK, that makes more sense; both are B&S products Intrimics are quite expensive even used and of quite limited range I see lots of them on E Bay and wonder if they ever sell them at the (wished for) prices.  They are not a tool that the average machinist or even tool maker would be able to afford; I'd think only an inspection department of a wealthy company or the government would have bought them.


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## Tony Wells (Feb 3, 2018)

They are quite handy for catching 3 jaw eggs on thin parts. I've got a couple stashed away someplace. But then, I was allowed to clean out some instruments from a company I worked for. I have a few things most hobbyists and even smaller shops aren't likely to have (Ultrasonic thickness mic, anyone? Profilometer?). I didn't get everything I wanted, but some interesting stuff nonetheless.


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## magicniner (Feb 4, 2018)

Telescoping gauges are very useful and not too expensive for a decent set. 
You can often pick up a good bore gauge kit second hand for reasonable money, I found a good Baty kit for under £20 last year. 
I have an internal micrometer of this style but not this brand - http://www.chicagobrand.com/help/inside_micrometer_files/image002.jpg - which came with a setting ring, allowing you to set it and to practice your "feel", it gives very good results at the bore opening. 
Higher cost but brilliant are Diatest individual bore gauges and kits, they occasionally come up at reasonable prices (at least comparatively so for what they do), over a several years I managed to pick up a few sets for an average price around £60 along with extension and adaptor kits.


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## Redmech (Feb 4, 2018)

Saw a video of a guy using rectangular gage blocks in the center with round gage pins on the ends to measure larger internal diameters, very slick method to measure internally to a very high degree.


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