Categories: Shaft Alignment,Machinery Maintenance,Other Topics

Is It Mils, or Thousandths, or What?

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By on December 1, 2017

On occasion, we are asked, “What are these numbers on the screen?”  All our alignment tools (and most others) can be configured in Imperial or Metric.  Most US users use Imperial (inches, feet, and so on).

When we say, “Your laser displays in mils”, we’re asked, “What’s a mil?”

Definition – [mil] noun. 1. a unit of length equal to 0.001 of an inch.  It is a term normally used as a wire size, or in electronic measurements of length, such as calibrating probes.

So 1 mil, and (1) one thousandth of an inch (0.001”) are the same thing.  Well, why display it that way?  Good question!

In the photo below, the vertical offset reads -13.4 mils.

If it was displayed in thousandths, it would read -0.0134”.  It takes 5 characters to display it in mils.  It would take 8 characters to display it in thousandths.  Since there are eight alignment results on the screen:

  • Mils 8 x 5 = 40 characters
  • Thou 8 x 8 = 64 characters

Simply stated, it takes less characters to say the same thing.  Which means we can fit bigger numbers on the screen.  At my age, the bigger the numbers are, the better!

  • Another thing to consider; shims are measured in thousandths, but no one calls them by their proper name. I would never say, “Hand me a ‘zero point zero two five inch’ shim”.  I would say, “Hand me a 25.”
  • Same thing on a dial indicator. If I were checking runout, and my indicator went from 0 to +0.008”, I would say “plus eight”.

Mils?  Thousandths? – they are the same thing.


About the Author

Stan Riddle joined VibrAlign in 2008. He has over 35 years experience in aligning industrial machinery. Stan received his AAS Degree in Machinist Technology from Surry Community College in Dobson, NC, and also holds a diploma in Industrial Systems Technology from Forsyth Technical Community College in Winston-Salem, NC, where he was also an instructor in the program.

Stan began his maintenance career working as a machinist and millwright for companies such as Weyerhaeuser, R.J. Reynolds, and Tyco Electronics. He also has over 25 years experience in Predictive Technologies, such as vibration analysis, thermography, oil analysis, and ultrasonic inspection. He is a certified Level III Vibration Analyst with the Vibration Institute, and is a Past Chairman and Board Member of the Piedmont Chapter.

Stan and his wife live in Yadkinville, NC.

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