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.

Related Terms

  • Interchangeable Products
  • Parameters
  • Revision
  • Reidentification
  • Manufacturer’s Part Number (MPN)
  • Assembly Revision