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Let's Talk Precision Measuring Tools

It has occurred to me there has not been a thread here about precision
measuring tools. Back in the 70's I worked for the Astrogeophysics Instrument Shop at the University of Colorado. I got introduced to all kinds of precision stuff, including measuring tools. Back then even the cheapest stuff cost more in actual dollars (not adjusted for inflation) by FAR than it does today.

I hope this thread might serve as a place we can show the various precision measuring tools around, and maybe give newbies some idea of the cost and utility of each.


I will try and find some pix of this.... but believe it or not a thin string of plastic is a measuring tool. In the case of a bearing (like a rod bearing or main bearing) you put the string across the bearing surface at right angles and torque the bearing down... then you open it up and measure the squish - eg. how WIDE is the little string of plastic once it has been squashed? The gauge is the paper the string comes in!


This one measures from .001 to .003 by gauging the width of the "squash". Perfect cap main bearings and rod bearings in an engine.

It is incredibly precise and has been used for over 50 years, unchanged. So the first tool isn't a tool per se... But is a tool. A precision one.


let's start by looking at the nuts and bolts of measuring tools... here are a few...


What you are seeing is a dial caliper (digital version) on top...two micrometers, old style, on right...expanding bore gauges at bottom, and on the left is a depth micrometer. Let's start with the most versatile of all precision tools in my mind... the caliper...



In the old days they were like a slide rule... stamped steel


they had what was called vernier markings, and you could "guess" at the accurate measurement by what line was the one aligned


cost back then in 70's dollars ? About $15-20.

Then we had dial indicator types.... here is a 70's model made of composite material. Cost in the 70's ? $20-40... a bargain. My first and I was excited...


In order of magnitude is was ok within plus or minus a thou or two....(a pretty rough measurement)

Then there was the stainless dial model...



Cost in the 70's nearly $75.

To read it, you had to see the tenths bar on the slide and then add the gauge... here we know we are between .400 and .500..


this reading? Can you guess?


did you guess 0.574 inches?

The caliper measures not only internal thicknesses (like diameters) but can measure bore sizes (assuming they might be uniform - unlike a cylinder in an engine) and also measure depth too! (Not crazy about this depth part of this one though, too big !)


* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

Enter Asia into the market in a big way... In the 1990's cost of a Digital model of a caliper fell from hundreds into way under a hundred. Today they can be had for less than the cheap vernier models in the 70's - UNADJUSTED for inflation.

Here is a $20 current model


Whereas back then there was no reason to spend the $$ for an expensive tool you might not use, today there is no reason NOT to have one. They can measure outside diameters, inside diamters and depth, all in one tool. (pics coming of each function)


Long thought of as THE precision tool. They measure by rotation of a thread. In fact here is a little quiz. If each revolution is .025 inch.... what is the thread pitch? Think....

(A. 40 TPI)

Micrometers only measure outside measurements and are not as versatile as a caliper. A SET of 3 can be had for under $30 these days on sale.... and they have carbide tips (no wear point) and are accurate to under a thousandth, closer to a ten thousandth. BUT, you will need to learn to read them. (If there is interest I can do a thread on how to read an old fashioned micrometer gauge).

Digital models exist for about twice the price of the old style. Much easier to read. Here is the set I own. Notice my name on them? This set has been stolen, recovered and returned to me!




More or less a micrometer without the anvil.... you use it to measure the depth of things. Usually sold as a set with replacement rods that allow meaurement to a depth of 4 or 6 inches.


My set, can you guess what lengths predominate my usage ?


The digital caliper does this just as well. Still, of my precision tools I love my old depth micrometer. It is just a pretty tool. Oh and while we are here, let's look at the markings on the shaft, all about how you read one...



The dial indicator is a tool that displays on a dial face the extension of a rod. As such it can be used in dynamic environments to display changes in measurement, as in runout on a rotor for example. Inexpensive 0.0 to 1.0 inch indicators can be had for under $15 today. The base to hold them costs as much. Here is one such import:


Recently I picked up a digital version of this dial indicator - for $22!


A dial indicator and a magnetic base are valuable tools, next right after the dial/digital caliper in my book.



There are tools that do not measure per se, but all you to gauge something and then measure the gauging tool for a final number.... for bores, you can use expaning collets for small ones (no pics as I do not own a set) and for larger bores, expanding gauges


These are spring loaded gauges you compress (arrows show in and out movement of the business end), and then lock in place by tightening the nut at the end of the shaft (single arrow). You unlock and move around to gauge the bore, and then tighten the securing nut and remove and measure THIS tool with another precision measuring tool. I paid under $20 for the set.


Also plain calipers, inside and outside will do the same thing..

(pic forthcoming)


These are the plain Jane of precision measuring tools.... next to plastigage. They consist of flat steel (or stainless or brass) feels of measured thickness. They act in most cases as "go" or "no go" tools. The last one that fits is the measurement, more or less. In the days of points in distributors they were in every tool box. I see them less frequently today. Wire versions are used to measure spark plug gaps.

(pics coming)


EF Tranny Guru
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These are transmission clutch pistons, and I need them thinner to add more plates... like .050 off one face kinda stuff.

and they come only come in aluminum...


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Glacier, how did you recover your stolen micrometers? Did somebody try to sell them on EBay, and then you saw it? I've had a lot of things stolen in the past, and was never able to recover anything. This should be an interesting story.


EF Tranny Guru
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At the risk of hijacking my own thread....

This was about 3 or 4 years ago. I had moved in with my then GF. One night we came home from a play and had left the key to the house/garage door in the house.... so we exited the garage door and she put the garage door opener in her purse.... well it retriggered the garage door and opened it, so it was open all night.

The next AM as I was leaving for work it was apparent we (or more appropriately *I*) had been burgled. The thief took about $2000 worth of tools.... and $1000 worth of other things.

I called the sheriff and they sent someone out to take a report. I missed half a days work. I figured all my stolen stuff was gone.... Including some brand new never used paint guns - that I had inscribed with my driver's license number. and phone number. In fact an unused brand new $300 Sharpe Platinum gun was among those stolen, as was a $15 HF detail gun. With the Inscriptions mentioned.

Fast forward. Several days later, Sat am 6AM. Doorbell rings. Sheriff's officer with a rubber gloved hand holding the HF $15 detail gun at the door. (Found me thru my ex wife and the old phone number - geeze) standing there. "Can you identify this , sir?" he asks.

I did and the *******, a parolee, went back to prison for 18 mos. THAT was the easy part.

Next I was invited to the sheriff's impound place to identify MY stuff. I recovered some but not all of it. BUT, the micrometers? He had not gotten to them yet (he had been busy grinding off and obliterating my inscriptions on metal) So they were easy to identity. I had to wait until he made a plea deal and went back to prison to get my stuff back. (4 mos)

Thus endeth the case of the purloined micrometers.