Top 16 Types Of Micrometers (Screw Gauge)

1. Inside Micrometer

Inside micrometers are commonly used to measure large internal diameters. Though they work equally effective at measuring the inside diameters of holes and registers. Their shape resembles a pen and has a thimble in the middle that can be rotated. The micrometer expands whenever the thimble is rotated. Thimble will expand until it touches the inside of the pipe and a numbering system is used to get the measurement on thimble. In this micrometer, good quality steel is used for spindle and measuring head. Required for high grade steel face tools.

2. Outside Micrometer

Outside micrometers (external micrometers) are used to measure dimensions of small components and require a relatively high accuracy. These micrometers supply direct readings. They are manufactured in different model to suit different applications.

These micrometers are used to measure the workpiece external dimensions.

3. Differential Screw Micrometer

The precision of a differential screw micrometer is higher than standard micrometer because it uses the differential screw concept. In this micrometer, the screw has two type of pitch, one smaller and one larger, rather than a uniform pitch as in a standard micrometer. Both screws of the differential micrometer are right-handed, and the screws are positioned so that when the thimble is rotated, one goes forward, while the other goes backward. The anvil is not linked to the thimble; instead, it slips into the sleeve. The smaller screw nut is attached to the anvil, the bigger screw nut is attached to the sleeve, causing the screw to rotate with the thimble.

4. Universal Micrometer

This micrometer type has an interchangeable anvil such as spherical, flat, disk, spline, blade, knife edge and point. They are called universal micrometer because their structure consists of modular components that allow a micrometer for multiple-functioning, that is, as a depth micrometer, outside micrometer step micrometer etc.

5. Blade Micrometer

This micrometer includes a narrow tip matching set which help it for the measurement of o – ring groove which is a narrow groove.

6. Screw Thread Micrometer (Pitch Diameter Micrometer)

These micrometers have thread tips that are properly shaped to measure the pitch diameter of screw threads and they are very accurate. They are very similar to ordinary micrometer the only difference is that they have special spindle and anvil. The internal vee anvil has which can fit the thread and can rotate freely, so the vee can adjust to various rake range of thread. The spindle has ground cone shape and when it is in contact with the anvil the micrometer measures zero regardless of the need to be measured, various types of anvils are provided.

7. Limit Micrometer

The limit micrometer has two spindles and two anvils and they are used as a quick measuring instrument. Component are inspected and must pass with first gap and stop at second to fully satisfy the specification criteria. The two gaps accurately represent the bottom and top rage of tolerance.

8. Bore Micrometer

These micrometers typically include three anvil heads on the micrometer base that are used to accurately measure inside diameters.

9. Ball Micrometer / Spherical Face Micrometer

These micrometers have their anvils of spherical or ball shape. They can have a ball anvil and a flat anvil and they are used to measure the thickness of tube wall, distance of edge to the hole, and the distance of the anvil on the round surface. Ball micrometers have a different application than the tube micrometer because tube micrometers are used to the measure round surfaces instead of tubes, but ball micrometer are cannot fit in a small tube. Ball micrometers can be used with a pair of balls for single tangential point contact requirement on both sides. In general, these are used to measure the pitch diameter of the screw thread.

10. Bench Micrometer

These micrometers are used for the high precision inspection and accuracy work about half a micrometer. This micrometer is based on the principle of magnifying technique and the 0.01 mm spacing between anvils are equal to graduated width of thimble of 1 mm. So, the actual distance is magnified by 100 times. It is possible to modify the larger thimble diameter.

They provide better accuracy because large diameter has large number of divisions in large circumference. Their advantage is that the effect of the error is very small.

The only disadvantage in bench micrometer is that they can only be used for comparison purpose and are very sensitive.

11. Digital Micrometer

These micrometers use encoder for the detection of the distance and then display result to the digital screen. To avoid the human error in the measurement of the dimensions, the digital micrometer is used for the purpose. The digital micrometer gives direct reading of the measurement.

12. Depth Micrometer 

These types of micrometers are used to measure the depth of slots, holes and recessed areas. They have a shoulder that can be used as a reference surface and they are held securely and orthogonal to the hole’s center line. For the measurement of large ranges, it is necessary to use extension rods. Screw in various micrometer depth gauge from 20 mm to 25 mm. The length of micrometer depth gauge can vary from 0 to 225 mm. The extension rods are inserted from top of the micrometer and the rod is marked between each 10 mm, so they are clamped into any position.

13. Thickness Micrometer

These micrometers are well suited for the measuring cylinder or sleeve as they cannot be measured from conventional micrometer. Therefore, they are used to measure thickness of cylinder wall. For this purpose, an anvil is provided in which the spherical measuring surface of frame is cut on outside for allow the anvil in the diameter tube, minimum diameter from 5 mm. the shape of the anvil is cylindrical and the axis of the anvil must be orthogonal to the axis of the spindle. Therefore, the thickness micrometer is widely used to measure tubes with an inner diameter less than 12 mm.

14. Vee-Anvil Micrometer

The outside micrometers are the ones in which a small V – block is provided for anvil. They are used to measure the diameter of circle from three different points equidistant around the micrometer. For example, they are used to measure the diameter of 3 flute twist drills and end-mills.

15. Tube Micrometer

16. Vernier Micrometer

This micrometer has highest accuracy in the micrometer group. It can measure with 0.001 accuracy. The main scale is classified by two sets of division markers on the barrel. The set to the left of the reference line reads in mm, while the set to the right of the line reads in 1/2 mm.

A thimble scale has 50 equally graduated divisions on the thimble. Each thimble division represents 1/50 the minimum division of the main scale. 1/2 mm is the smallest division value on the main scale.

On the sleeve, there is a vernier scale. The vernier on the sleeve has ten divisions, corresponds to nine divisions on the thimble. As a result, one division on a vernier scale equals 9/10th of a thimble. However, on the thimble, one division equals 0.01 mm. As a result, on a vernier scale, one division equivalent the least count of a micrometer.

Count at least = value of one division of thimble – value of one division on Vernier = 0.01-0.009 = 0.001.

Notes when reading micrometer

• The micrometer comes in a diversity of sizes and ranges, and the appropriate micrometer should be selected based on the size of the workpiece.
• Dust must be removed from the micrometer, and the spindle must move freely.
• Before measuring, check and set the reading to zero.
• The workpiece to be measured should be held in the left hand, and the micrometer should be held in the right hand.
• Make sure that the measured dimensions are parallel to the spindle and anvil axes.
• When making final adjustments, constantly use the ratchet, when collecting readings, constantly use the locknut.
• When measuring diameter, ensure the anvil and spindle sides only in contact with the maximum dimension.