It is common in manufacturing to produce parts that must integrate with one another to serve a common purpose or perform one or more operations. How these items interact is extremely important, and will affect the overall functionality of an assembly. The relationship between two mating components is known as “fit”, and pertains to how tight or loose the items should be when joined together. There are three types of fit commonly referenced in manufacturing and mechanical engineering.
Clearance Fit
Clearance fits allow for loose mating, where free movement is important and a certain amount of play is desired. We see clearance fits called for where elements should be able to slide in and out without obstruction, and where alignment can be loosely guided but does not require tight precision. Examples of clearance fit might include bolt/shaft holes where an element will slide freely through another feature.
Interference Fit
An interference fit will be much tighter than a clearance fit. Also referred to as a press fit or friction fit, the interference fit requires some degree of force to join two components. Pressing a bushing, bearing, dowel pin or other items into their mating components are all examples of how an interference fit can be used. Once joined, this creates a relatively solid union that would require substantial force or potential machine operations to uncouple.
Transition Fit
A transition fit would fall between a clearance and interference fit. Transition fits are called for when accurate alignment is critical, and mating parts must join with greater precision. You may also see these referred to as a slip or push fit. There will still be a greater degree of clearance than a press/interference fit, but it will be substantially smaller and should remove excess play or movement in the joint.
