Starrett - Outside Micrometers

No. 221 Hi-Precision Micrometer permits direct readings in ten-thousandths of an inch (.0001") without a vernier, plus automatic control of spindle pressure.

This micrometer features a black graduated inner thimble and sleeve reading in thousandths and a red graduated outer thimble and sleeve with large, widely spaced graduations which give direct readings in ten-thousandths.

It also features an exclusive constant pressure mechanism which eliminates "feel" and automatically insures consistent spindle pressure for every measurement. Extremely easy to use.

Readability Features

• Precise instant, direct readings in ten-thousandths of an inch (.0001") – no vernier readings necessary
• Gives constant spindle pressure for all readings
• Starrett satin chrome finish – no glare – resists rust
• Advanced sleeve design with staggered lines and distinct figures for precise and easy readability
• Convenient decimal equivalents on Inch tools

Ease-of-Handling Features

• Balanced frame and thimble design insure easy handling and better readability
• Ring-type knurled lock nut for quick and sure locking
• Gracefully designed tapered frame for use in narrow slots and tight places

Accuracy and Long-Life Features

• Rigid one-piece frame of drop forged steel
• Extremely hard and stable one-piece spindle (the heart of our accuracy)
• Micro-lapped measuring faces
• Quick and easy adjustment
• Starrett workmanship

How to Read a Starrett Hi-Precision Micrometer

This micrometer is accurate within .00005" throughout the range.

(1) Using the micrometer conventionally, bring the measuring faces up snug to the piece being measured, and then "load" the micrometer by continuing to rotate the red graduated thimble through ten of its divisions. (There are four equally spaced red reading lines on the .0001" reading sleeve and four sets of numbered red graduations on the .0001" thimble reading zero to nine. This allows you to read the .0001" graduations no matter what position the micrometer is held.)

(2) Hold this "loaded" position and now observe the black .001" graduations on the inner thimble in relation to the reading line on the sleeve. Slowly let the red graduated thimble return until the first black thimble graduation aligns with the black reading line on the sleeve. Now hold this position with the black graduations aligned.

(3) At this point the black graduations will be your .001" reading and you can then take the .0001" reading directly from the red graduated thimble as it lines up to the red reading lines at any one of the four positions, and add it to the .001" reading.

CAUTION: Do not force the red graduated thimble if you feel it hit the stop. Also, do not at any time let the red graduated thimble snap back from its "loaded" position. Damage could occur due to either circumstance.

Hi-Precision Micrometer- No. 221 Series
Range: 0-1"

J.W. Donchin Co.
Ph: 773-261-2182 • Fax: 773-261-2867 • Email: sales@jwdonchin.com