A term that is applied to the tightest fit between two parts is ____.

Regardless of Feature Size (RFS) is the default condition of all geometric tolerances by rule #2 of GD&T and requires no callout. Regardless of feature size simply means that whatever GD&T callout you make, is controlled independently of the size dimension of the part.

This rule can be overridden by Maximum Material Condition or Least Material Condition, which specify the GD&T conditions at the Max or Min size of the part. LMC or MMC must be called out on the drawing specifically though to eliminate the regardless of feature size default.

For simplicity, the definitions of all the GD&T symbols are by default, stated as Regardless of Feature Size. For most geometric symbols besides those that allow maximum material condition, RFS can never be overridden. Regardless of feature size eliminates any potential bonus tolerance, allowing the GD&T tolerances to be more tightly controlled.

Reason for Use:

Since Regardless of feature size is the default condition it is used always and ignored only when specified. It is applied for most part conditions. RFS is always kept where balance is critical and where both sides of the tolerance must be maintained independently of the GD&T callouts.

Regardless of Feature size requires the axis to be measured separately from the size of the hole and cannot be gauged easily. However, there is no bonus tolerance allowed in this condition so the perpendicularity would be much better controlled regardless of the size of the hole.

In the following example, no material modifiers are called out, RFS would be implied and the control for the parts would be like this:

This of course makes sense and follows the normal rules of GD&T. However if you were to add a Max Material Condition to the drawing, the hole limits are quite different. If you were to control perpendicularity of an axis with MMC, you could control and gauge the part according to Example 2 from our perpendicularity page:

There is now a bonus tolerance that is added to the perpendicularity tolerance to make it larger. With Regardless of feature size this could not happen, as the perpendicularity would have to be the same, regardless of the features size. This is a fairly advanced concept and is better explained in our section on Bonus Tolerances (coming soon).

Measurement/Gauging of Regardless of Feature Size:

Gauging and measurement would apply as normal for this condition for any GD&T symbol. All GD&T callouts must be measured independently from the size of the part.

Learn GD&T at your own pace and apply it with confidence in the real world.

All Symbols

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.