Which Starrett Micrometer, When?

Which Starrett Micrometer, When?
starrett micrometers

In this post, we'll discuss what micrometers are used for, and some of the most popular types of Starrett Micrometers and their application.

What is a micrometer?

A micrometer is a precision measuring instrument that measures small distances or thicknesses between its two faces, one of which can be moved away from or toward the other by turning a screw with a fine thread. Micrometers are precision measuring tools that can obtain precise measurements on extremely small objects, and are widely used in engineering, for inspection tasks and any application or industry that requires high accuracy and precision. 

What Is Each Micrometer type used For?

Outside Micrometers

The outside micrometer (OD) is the most commonly used type of micrometer. Outside micrometers are used to measure external dimensions such as the outside diameter of an object. Used for the accurate measurement of small components in mechanical engineering and machining as well as most mechanical trades, the outside micrometer consists of a U-shaped frame, a screw mechanism, and an anvil. The object to be measured is placed between the spindle and anvil. The spindle is moved by turning the ratchet knob or thimble until the object to be measured is lightly touched by both the spindle and anvil.

Starrett Series 230 Outside MicrometersOutside MicrometersStarrett 230 Series Outside Micrometers reach most places others cannot. In addition to a 0-1" measuring range, the Starrett Model T230XFL Outside Micrometer features:

Outstanding Readability: the satin chrome finish is anti-glare and rust resistant. With staggered lines and distinct figures, the advanced sleeve design offers precision and is easy to read.

Ease Of Use: the tapered balanced frame is gracefully designed for use in narrow slots and tight spaces common in machining, manufacturing and other industrial environments.

Unparalleled Feel: with a choice of friction thimble for uniform pressure, or the combination ratchet and speeder for uniform pressure and quick adjustment along with the ring-type knurled lock nut for quick and sure locking, the Starrett Model T230XFL Outside Micrometer provides smooth operation and outstanding handling.


Inside Micrometers

Designed to measure the internal dimensions of an object, such as the inner diameter of pipes, cylinders, or bores, internal micrometers consist of a cylindrical rod and a screw mechanism that expands outward, inside micrometers measure the inside, or inside diameter (ID) of an object. Inside micrometers resemble a pen, but are equipped with a thimble in the middle that turns. As the thimble turns, the micrometer expands until each end of the tool is touching the inside of the pipe. You then use the numbering system on the thimble to find your measurement.

Starrett 128BZ Inside Micrometer Set


Starrett produces a number of differing inside micrometers with rigid, tubular steel rod extensions that allow for measuring up to 7350mm, among the most popular being the Series 128 Inside Micrometer Sets. The Starrett 128BZ Inside Micrometer Set features a 6-150" range and .001" reading, with outstanding lightness, rigidity, and ease of use. Additional features include:

Easy Handling: Balanced design for better feel and accurate measurement.

Durability: All rod anvil contacts are hardened and ground for a longer life.

Outstanding Readability: the satin chrome finish micrometer head is anti-glare and rust resistant. With staggered lines and distinct figures, the advanced sleeve design offers precision and is easy to read.

Firmer Rotation: this limits the tendency of the micrometer head to rotate when being withdrawn from the workpiece.


Depth Micrometers

A depth micrometer is used for measuring the depth of a hole, recess or slot. Depth micrometers have a base that aligns with the top of the recess that needs to be measured. The thimble is on a shaft that sticks up from the base. As the thimble turns, a measurement rod comes down from the shaft. Turn until the rod hits the bottom surface of the hole being measured, then use the numbering system on the thimble to find your measurement.

Starrett offers a varied line of depth micrometer, electronic, mechanical, digital and regular with one or two shoulders and can measure depths up to 225mm using the easily adjustable extensions rods.

Starrett 449BZ-6R Depth Micrometer


The USA-made Starrett 449BZ-6R Depth Micrometer has a 0-6" range, .001" reading, and a base shape designed to automatically position the fingers so that it is easily held in place for stability. The reading surface is again finished in the satin chrome. Additional features include:

Non-rotating Blade: In operation, the blade does not turn, but moves perpendicularly only, permitting depth measurement of narrow shoulders without the blade rolling off.

Easy Handling: Combination ratchet and speeder for uniform pressure and quicker adjustment.

Versatility: the depths of holes, slots, shoulders and projections can be measured with this fine tool.

Durability: features a hardened, ground and lapped face and hardened rods.


Bench Micrometers

starrett bench micrometers

Bench micrometers are especially suited for high precision measurements where the workpiece must be brought to the gauge. Bench micrometers are best suited for bench use in a shop environment or an inspection laboratory.

The workpiece is staged between the anvil and spindle on an adjustable table, which can be raised and lowered to a selected height and locked in position by turning a knurled thumb screw on the back of the base. The base is made of cast iron and heavily proportioned to sustain gauge accuracy and assure stability when in use. Please contact our metalworking team for assistance selecting the right bench micrometer for your shop.


Starrett offers a wide variety of micrometers, available in electronic, digital and traditional vernier models, with varying sizes and accessories.  For assistance selecting a micrometer, contact our metalworking team or give us a call!

Want more information on Starrett Micrometers?Starrett-Micrometer-Guide-1

Download the Starrett Micrometer Guide for an in-depth explanation of micrometer features and components, step-by-step instructions on how to read a micrometer and how to adjust a micrometer, plus measuring tips from the precision measuring experts.