What is Form, Fit, and Function (FFF)?

Form, Fit, and Function Definition

Form, fit, and function (FFF or F3) define the parameters that set the characteristics of a part:

  • Form: The shape, size, dimensions, mass, weight, and other visual parameters that uniquely distinguish a part.
  • Fit: The ability of a part to physically interface with, connect to, or become an integral part of another part.
  • Function: The action or actions that a part is designed to perform.

When you consider whether to introduce a new part number or create a new revision for an existing part number—it’s important to consider and follow the form, fit, and function guidelines.

What is Form, Fit, and Function


What is the difference between form and fit?

The shape, size, proportions, mass, and other visual characteristics that distinguish an item are referred to as form. This determines how the part or object “”looks.”” The capacity of an object to physically interface with all other components is referred to as fit.

*Source: https://www.technia.us

What is form-fit-function data?

Data relating to items, components, or processes that are sufficient to allow physical and functional interchangeability, as well as data identifying source, size, configuration, mating and attachment characteristics, functional characteristics, and performance requirements, is referred to as form-fit-function data.

*Source: Resource Article: Form, Fit, Function

What is form-fit-function change?

Form, fit, and function guidelines define how far subsequent revisions of a part can differ from the original before new part numbers are assigned. This is crucial for guaranteeing that components may be swapped out without difficulty.

*Source: https://www.technia.us


Enforcing form-fit-function rules helps avoid manufacturing delays, but these rules need to be revised when parts deviate from the original design. This article goes over how to handle form-fit-function changes to maintain manufacturing efficiencies.