If you work in an industry where precise measurements of tubes, pipes, and valves are taken occasionally, then there’s no doubt you’ll have to turn to a micrometer. These tools are hailed for their efficiency and high accuracy. Now, if you’re an intern, choosing the right micrometer to take specific measurements can be really confusing. Since these measuring tools are categorized into three main sub-divisions, this post will try to give a clear inside micrometer definition to help any novice understand this tool right from its core.

Now, if you happen to see the micrometer for the first time, I believe you’ll say it resembles one of the tools found in a medieval torture chamber. With its complex design and multiple calibrations that seem not to make sense, any novice will stand to wonder why this tool is so special to every veteran engineer and mechanist out there. So, if you’re reading this post and you’ve been wondering the same, then I’ll take you through a quick lesson on micrometers, and most specifically, the inside micrometer.


What is a Micrometer?

A micrometer is a device that’s specifically used to measure distances and diameters of very tiny objects. Also known as a micrometer screw gauge, this device is unbelievably precise. Its ability to accurately record microscopic measurements up to one-thousandth of an inch makes it one of the best tools every professional engineer and mechanic can’t work without.

Micrometers come in three main categories to suit every need and purpose. These include the outside micrometer (usually used for measuring the outside diameter of objects), the inside micrometer (for measuring the inside diameter of tubes) and lastly, there’s the depth micrometer (that’s used for measuring the depth of holes and slots).


Anatomy of the Inside Micrometer

Now, just as its name implies, the inside micrometer is specifically designed to measure the inside diameters of tubes or the distance between two parallel objects. It’s mostly used in the engineering, plumbing, and mechanic fields to measure the diameters of tubes, wearing rings, cylinders, bearings, and bushings.

The inside micrometer doesn’t come alone. For it to perform efficiently, there are a couple of attachments you’ll find in the package such as a micrometer head, extension rods (also known as spindles), the handle, and the spacing piece.

Since this type of micrometer is tasked to measure tubular pieces with varying diameters, the package comes with several extension rods with varying sizes to make it easier for you to measure any diameter of your choice.


Types of Inside Micrometer

Before we discuss the various parts of the inside micrometer, allow me to mention that this type of micrometer usually come in three different sub-divisions. These are the tubular, caliper-type, and bore micrometers. Although they all perform the same job of recording measurements, each one of them is designed to take a fairly limited range of measurements which makes them unique in their own ways.

Other than these three sub-divisions of the inside micrometer, there are two more categories you’re likely to come across to which are the standard and the digital inside micrometers. Standard micrometers on their part are read by examining the readings on the barrel and thimble.

Digital micrometers, on the other hand, operate the same way as their standard counterparts only that the readings are displayed digitally on a tiny LCD display on the barrel. So, with that said, let’s discuss just a little bit about the different types of inside micrometers.


  • Caliper Type Micrometer

Now, the caliper type micrometer looks just the same as a contemporary caliper with a few minor differences. Instead of the obvious anvil and spindle found in calipers, this one has two jaws instead that are inserted inside an object to measure its diameter. One of the jaws is stationary while the other is movable. The movable jaw is the one that is extended using the ratchet to fit inside a tube to measure its internal diameter. This type of inside micrometer comes in two variants which are the standard and the digital version.


  • Tubular Type Micrometer

Tubular micrometers are some of the most popular designs you’ll find in the market. Instead of the C-frame found in caliper-type micrometers, these ones rely on a thin tube that’s inserted between the hole or the ring being measured. Once you insert it, extend the length of the tube until it gets to contact with both ends of the object being measured. From there, measure the inner diameter of the object. Unlike the caliper-type, the tubular micrometer comes with a range of extension rods that can be used to cover a wide range of measurements.


  • Bore Micrometer

Also known as the bore gauge, this type of micrometer is in the family of the inside micrometers as it’s used to measure the internal diameters of pipes, holes, and cylindrical objects such as engine cylinders. This type of micrometer only has an anvil that extends to reach the depth of whatever is being measured. It comes in three major sub-divisions which are the dial, mechanical and digital.


Parts of an Inside Micrometer

Now that you’ve learned a lot about the inside micrometers, our last section will cover the important parts of this specific micrometer to help you understand how it works and most importantly, how to take the readings.

  • Micrometer Unit

The micrometer unit is also called the measuring head. Made of steel or any other hardened material, this part is the one that bears the scales which you’ll need when recording measurements. It usually has a main scale located on the sleeve barrel and a secondary scale located on the thimble barrel. When taking measurements, an adjusting screw is provided to allow the thimble to retain its tightness for accurate readings.

  • Extension Rods

Extension rods are also very common with inside micrometers especially the tubular variants. Also made of high-quality steel material, these rods come in varying lengths to make it easier for you to record readings both on shallow and deep cylinders. Extension rods can have their own measuring anvils or they can allow a variety of different anvil pieces to be fitted depending on the situation.

  • Handle

Lastly, there’s the handle. Although it’s quite rare to use the handle, it’s one of the most essential units that can really prove helpful when taking measurements of objects that are beyond 50mm deep. Since the micrometer head will need to be lowered deep inside the object, the handle will make it easier for you to hold the micrometer when recording readings.



As you can see, there’s a lot to discuss regarding the inside micrometer. There are three major sub-divisions of this type of micrometer with each designed to meet a specific measuring goal. So, if you’re an intern whose career requires you to use the inside micrometer, then this guide has offered you some inspiration that might help you throughout your long working career.

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