What is the difference between COTS parts and custom parts?

There are two kinds of components in any hardware product. 

• “COTS parts”: These are parts you can buy off the shelf. M2 hex screws are COTS parts. Standard metal gears are COTS parts. Standard switching power supplies can be COTS parts. 6′ USB-A to micro-USB cables can be COTS parts.  Of these parts:
  • Some parts are commodity items – fasteners, for instance, are low cost, and there are many places you can buy them from.
  • Some parts are critical to the performance of your product. For instance, a Coretex M3 microprocessor is a critical component. A specific Bluetooth low energy chip is a critical component. A specific motor designed into your drive chain is a critical component.
• “Custom parts”: these are parts that are unique to your design, that you will need to find a supplier to create specially for your product.  There are several categories:
  • Electrical / electronic parts: these include custom printed circuit board assemblies (PCBA), cable harnesses (i.e. custom cables with connectors on either side made to your specifications) and the like.  Of note: touch screens, although ubiquitous in modern society, are frequently made to order custom parts.  Why? Touch panels are bonded to display glass to order, for things like iPads and iPhones.  The chances of your design exactly matching that of an existing product is basically zero.  So if you design a beautiful installation-style display with a 21″ touch panel, it will be a custom item that you will need to find a strategic supplier to produce for you.
  • Mechanical parts: these can include plastic parts and metal parts, which can adopt a variety of shapes and have a variety of performance requirements (indicating a variety of manufacturing processes that can create those parts successfully.)