Classification of Assembly Fits in Metrology

Measurement and assembly classification in Metrology

The degree of snugness or slackness between mating components is used to categorize fits. The most common ways in which fits are categorized in metrology are as follows:

When two mating pieces have some space between them, this is called a clearance fit and facilitates assembly and movement. In applications requiring relative movement between the pieces, such as sliding or rotation, this sort of fit is commonly employed. In an interference fit, one or both of the mating pieces are fabricated to be slightly bigger or smaller than their nominal size to provide a press fit. Press fits and shrink fits are common examples of uses for this sort of fit when it is necessary to permanently attach the parts.

A transition fit is a form of fit in which the mating parts have both a clearance fit and an interference fit at different points. This form of fit is commonly employed when a certain amount of play is required between the parts, yet they must still be held securely.

A force fit is a sort of assembly in which the components are intended to be pressed or forced together to form a snug and secure connection. Use this form of fit when you need to make sure the pieces stay put, like in a bearing or shaft assembly.

In a locational fit, the mating components are planned to go into a particular spatial arrangement when assembled. When alignment is critical, like in a key and keyway assembly, this type of fit is used.

As a whole, metrology relies heavily on the classification of fits to guarantee that all components of an assembly are built to the appropriate tolerances. Choosing the right sort of fit helps engineers and designers guarantee the assembly will function reliably and achieve the specified performance objectives.

Video 1: Fit and Types of Fits – Clearance Fit / Interference Fit & Transition Fit (Animation)