How to Use Micrometers

How to Use Micrometers

Micrometers are devices for accurately measuring minute distances; modern gadgets are accurate down to one ten-thousandths of an inch. Depending on the application, they may be table top instruments or small hand-held tools. Micrometers are applied to measure the outside diameters; inside diameters; the distance betwixt parallel surfaces; the depth of holes, slots, counterbores, and recesses; and the distance from a surface to some recessed part.

Micrometers are available with metric and imperial graduations.

The micrometer consist of a semicircular frame having a cylindrical extension, the barrel (sleeve), at its right end and a hardened anvil at the other end. The bore of the barrel (sleeve) is threaded and a spindle screws into the bore. The spindle carries a graduated thimble which turns at one with it.

Parts of a Micrometer


Parts of a Micrometer (detailed)


Measuring FACES

The measured items are put betwixt the measuring faces, the anvil and the spindle (also called - measuring rods). The ANVIL is the stationary measuring face against which parts are held until the spindle makes contact with the work.

The threaded SPINDLE is the moving measuring face of the gadget. The spindle extends from the thimble. As the operator turns the thimble, the spindle pushes the item to be measured against the anvil. The spindle holds the item snug against the anvil, and a reading is taken.


The thimble refers to the revolving portion of a gadget's handle. Twisting the thimble opens the tool's jaws for reading inside ranges, or extends a rod for calculations of outside ranges or depth. Markings on the thimble revolve along with the handle to align with the barrel's scale and provide a measuring.


The locking device secures the spindle and preserves the measuring so that the micrometer can be removed from the workpiece before taking the reading. Some of the gadgets have a lock nut (as shown), whilst others may have a locking lever.

SLEEVE (Barrel) scale

The barrel forms the uppermost part of the handle; the part closest to the frame's "U." The barrel is a cylindrical piece of metal, integral to the frame; the frame and barrel are molded as one piece. The barrel's circumference features marks that indicate a measuring. Because the micrometer-caliper measures on a micro scale, its calculations are often lengthy decimals. To save space on the barrel, the marks appear as whole numbers that refer to a legend printed on the frame's exterior. In case of the sub-division group - the Electronic Micrometers, (as in Fowler 54-860-241-0 model) the results are shown with mechanical numbers which roll over.

RATCHET speeder-stop

The ratchet speeder increases the speed at which the spindle rotates, so the space betwixt the anvil and the spindle is reduced more quickly than it would be if the thimble were in use. Using the ratchet speeder reduces the time it takes to use the gadget.

The ratchet incorporates a slipping clutch mechanism that prevents overtightening and aids the user to apply a constant measuring force to the spindle, helping to ensure reliable measurements. If the force were to be excessive then it would be possible to overstress the frame thus causing permanent damage to the micrometer which would in turn lead to incorrect readings being obtained. To overcome this problem the ratchet stop is fitted and this drives the thimble through a ratchet device.


The frame is the basic element of any micrometer-caliper. The frame appears as a roughly U-shaped piece of metal. Etched upon the frame's exterior is a legend, or list, explaining the graduations indicated on the tool's barrel. A handle protrudes from one side of the frame so that its appearance resembles a small scythe.


Types of Micrometers

There are three types of gadgets under consideration which are commonly utilized: the outside, the inside, and the depth micrometers.

Types of Micrometers

1. Outside Micrometers - are utilized to determine outer ranges, like the thickness of sheet stock or outside diameters of round stock. The screw thread type of a gadget is a type of outside micrometer applied to measure not only the diameter of screws, but also the pitch of their threads. The item to be measured is situated betwixt the stationary end of the gadget, called the anvil, and the moving end, called the spindle. A knob, called a ratchet, is turned, pushing the spindle against the item. The thickness may be indicated by a mark on a vernier scale or by digital display.

2. Inside micrometers - applied to determine the inner ranges of an item: the inner diameter of a tube, bushing, cylinder, etc. They consist of a gadget’s head, a set of extension rods, and in some cases a handle. The length of the head itself is what is measured, since it is situated within the diameter being calculated; the smallest heads available are one-quarter-inch. The extension rods are applied when the maximum length of the head is too small for the opening. The handle is utilized for inaccessible areas, and the diameter is read from a vernier scale or a digital display.

3. Depth micrometers are used for measuring the depths of blind voids, grooves, recesses, etc. A flat surface at the top of the hole is required for the micrometer base to sit on, and the micrometer should be held firmly in place for an accurate reading. The ratchet is turned until the spindle touches the bottom of the hole, and the depth is read from the vernier scale or digital display.

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Measuring Procedure

How to hold a Micrometer How to Hold a Micrometer

1. Situate the item whose length, diameter or thickness is to be determined betwixt the rods (spindle and anvil).

2. Turn the thimble or ratchet to close the rods around the item to be measured. The rods should lightly touch the item betwixt them but not clamp down on it.

3. Flip the locking lever to lock the rods in place.

4. Read the value just exposed by the thimble on the central line of the cylinder. This value is in mm (millimeters). Typically, there is a mark every half-millimeter, with the mm marks rising above the central line and the half-millimeter marks going below it. For example, you might note that an object indicates 12.5 millimeters.

5. Read the mark on the thimble aligned with the central line on the cylinder. This mark is in hundredths of mm. For example, you might read the figure 12 on this scale, indicating a reading of 0.12 mm. There are 50 such marks, meaning that each turn of the thimble corresponds to half a mm, the distance betwixt the upward and downward marks on the cylinder central line.

6. Add these values together. This is the measurement of the item betwixt the rods. In the example, you would add 12.5 and 0.12 to get 12.62 millimeters.


Proper Use and Care for a Micrometer

  • Be sure to unlock the locking lever before attempting to revolve the thimble.

  • Clean the measuring faces with a clean cloth before and after measuring. It is also a good practice to occasionally clean the spindle to keep any contaminants from being drawn into the sleeve.

  • Use the grip on the thimble when requiring a large amount of travel but as you come close to closing in on the item to be measured use the ratchet stop so as to not overtighten the thimble and give an erroneous reading.

  • When a gadget is at its minimum reading the horizontal line on the sleeve should line up with the ‘0’ on the thimble. If that is not the case it will be necessary to calibrate the micrometer by revolving the sleeve. Each gadget comes with a half moon adjusting wrench for this purpose. To make the adjustment simply puzzle the wrench to the side of the spindle and insert the small tip into the leverage hole. It will not require much effort to turn the spindle however there is sufficient resistance in the spindle so that it will never move on its own. Larger gadgets are supplied with standards to check for correct calibration. When checking, be sure to hold the standard squarely betwixt the anvil and spindle. To help with this try revolving the standard slightly with your fingers while gently turning the thimble as you close in on the standard.

  • Never leave a tool exposed in the hot sun (store it in a toolbox, in a quality shelf or a cabinet, that can be found and purchased in furniture stores) and then attempt a measuring procedure. This would also lead to an erroneous reading.

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