Measuring tools can be divided into three categories according to their main USES:

1. Standard measuring tools.A measuring instrument used as a standard for measurement or metrological verification.Such as measuring block, multi - edge body, roughness relatively sample block.

2. Universal measuring tool (or universal measuring tool).Generally refers to the practical measuring tools produced by measuring tools factory.Such as scale, tablet, view block, calipers, etc.

3. Special measuring tool (or non-standard measuring tool).It refers to the measuring tool designed and manufactured for the purpose of testing a certain performance parameter of steel parts.Such as internal and external pipe groove calipers, galvanized wire rope calipers, step distance gauge.

A measuring instrument that reproduces the quantity value in a fixed and fixed manner. Its characteristics are as follows:

1. The quantity value of the enterprise is reproduced immediately by itself, that is, the tolerance value of the measuring tool is the specific size of the quantity value of the enterprise, such as the quantity block itself.

2. Structure type generally has no measuring tissue, no indicator or component of fitness movement.For example, the quantity block is only a commodity that reproduces the quantity value of the enterprise.

3. Because there is no measurement organization, the measured value cannot be measured immediately if it does not rely on other applicable measuring equipment.For example, the measuring block should be suitable for interferometer, electronic optical meter.So this is a passive measuring device.