Gauge Blocks

Gauge blocks, also referred to as gage blocks, Johansson gauges, slip gauges, or Jo blocks are precision-machined blocks that purposely made for calibrating measuring devices and for use as precision measurements. They are commonly manufactured from steel but other materials such as ceramics can be used and come in sets featuring a range of industry standard lengths.

What are gauge blocks used for?

Depending on their grade, gauge blocks are used for precision measurements and for the calibration of precision instruments and machinery, they are the main means of standardising lengths in industry.

How to use gauge blocks

Blocks are removed from their set and stripped of their protective coating, usually oil and joined together in a process called wringing. Wringing is the act of sliding one ore more blocks together to form a stack to the desired dimension, typically using as few blocks as possible to reduce inaccuracies caused by the (minute) gap between each block.

Blocks are calibrated to be accurate at 20 °C (68 °F) this helps eliminate errors in accuracy due to thermal expansion, so it is ideal that this temperature is maintained during use.

Wear blocks are used at either end of the stack to help reduce the risk of damage to the blocks and negating their precise accuracy.

Types of gauge blocks

Gauge blocks come in different grades and commonly come in three different materials. Whilst their function is identical the material and grade of the block makes it suitable for different applications.

Standard grade - Standard gauge blocks are commonly made from steel and are most used in non-calibration applications. They are usually used in measuring industry standard lengths.
Calibration grade - These blocks offer greater precision and are made from harder materials such as ceramic or tungsten carbide as they incur less wear during use, and are less susceptible to corrosion, maintain greater accuracy.
Both types of gauge blocks are available in metric and imperial measurements.

Things to consider when choosing a set of gauge blocks

There are several factors to take into account when choosing a set of gauge blocks. To help with this process Cromwell has listed some common considerations, to help you select the right set for your needs.

Material - The material of the gauge blocks you choose can be important for several reasons, durability is one such factor. Blocks that are manufactured from steel