Fit, Form, Function Explained

Here at Vista Industrial Products, Inc. we encounter several instances where engineers run into issues engineering a part causing them to over engineer the part. One thing engineers need to remember is the fit, form, and function of the part. If it doesn’t need it for the fit, form, or function, don’t add it!

What is Fit, Form, and Function (aka F3)? Simply put, it is the identification and description of characteristics of a part, component, and/or assembly.

Fit: refers to the ability for the part to interconnect, mate with, join, or link to another part or an assembly. If a part requires “fit” it usually refers to having tight tolerances in order to match up to other parts or assembly.

Form: refers to dimensions, weight, size, and visual parameters of a part. This mainly represents to overall visual characteristics of the part.

Function: refers to the purpose of the part by how the part should perform and operate.

This information allows for the possibility of making certain changes to the part while keeping the fit, form or function. In other words, say if a part required a specific tool to fabricate it, but the manufacturer doesn’t have the tool in stock. Instead of investing in tooling, the manufacturer could find out the fit, form, and function of the part in order to determine if a tool in stock can be used as long as the necessary F3 criteria are met.

For example, say a chassis required air flow for the components that would be contained inside of the chassis. The function of the chassis is to hold the components inside as well as provide air flow to prevent overheating. For the air flow, the chassis required 32 staggered 1/8” round perforations. However, the manufacturer doesn’t have the correct tool pattern to punch this pattern, but has a tool that is 8 staggered 1/4” round perforations. Since the chassis’ purpose is its function, rather than the form or fit, changing the perforation pattern to the tooling the manufacturer has, would work just fine because it’s accomplishing the exact same thing by providing 40% open area for the air flow, but just looks slightly different, and costs a lot less than purchasing tooling to obtain the exact same function for what the chassis is meant for.

Original Perforation Requirement                            Adapted Perforation with same function

fit form function examplefit form function example for engineers

Fit, form, and function are also significant when changing the actual design of the part or component but keeping either the fit, form, or function the same. It’s important to keep in mind that the amount of acceptable deviation of the fit, form, or function needs to remain constant in order for the part to serve its purpose. This is also very critical when reverse engineering a part while making subtle changes.

For more information about our engineering capabilities or our metal fabrication capabilities, please visit Vista Industrial Product’s website.  Feel free to leave a comment or question regarding your engineering needs!

3 thoughts on “Fit, Form, Function Explained

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