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Different Types of Key Inserts

By STG Machine

STG Machine has covered many topics related to key inserts, so we thought it would be helpful to explain the different types of key inserts available. This article does not cover every type of key insert available, but it will give a detailed explanation on the main key inserts used in manufacturing.


There are 3 primary types of key inserts:

Thin Wall: These inserts are thinner, hence the name thin wall. They are primarily used on smaller holes or near the edge of a workpiece when space is limited.

Thick Wall: Thick wall inserts (otherwise known as heavy duty) have thicker walls than thin wall inserts and come with increased strength properties.

Extra Thick Wall: The largest and strongest of the inserts available are called extra thick wall or extra heavy duty. They are used to help reduce the size of tapped holes.


  • 303 Stainless
  • 304 Stainless
  • 316 Stainless
  • 17-4 PH Stainless
  • A286 Stainless
  • Nitronic 60 Stainless
  • 4140 Alloy
  • Inconel 718
  • Carbon Steel


  • Zinc Phosphate
  • Passivate
  • Cadmium
  • Dry-Film Lube
  • Silver
  • Nickel

Hole Condition:

Although standard key inserts are the most popular, there are four other configurations of key inserts available. Inserts are also available in floating, blind end, solid and cast-in configurations. Floating key inserts are usually used with sheet metal components due to their more forgiving tolerance requirements.

Blind end key inserts are just like ordinary inserts, but they have a designated depth. Since they are capped at the bottom they only allow objects to travel a specific depth.

Solid key inserts are actually solid pieces of mass that can be used to plug or fill a threaded hole. They can be used to plug or add material that can then be drilled or modified afterwards.

Cast-in key inserts usually come in a limited amount of sizes and they are most commonly made out of stainless steel and brass. They have a knurled exterior surface and primarily used in fixtures and molds when casted. 

Each of these different types of key inserts serve a specific purpose, and their use largely depends on your application.

Self-Locking vs Non-Locking:

Just like with helicoils, you can purchase self locking and non-locking key inserts. They serve the same function as any ordinary self locking hardware and they allow screws to be fixed in place. Key inserts usually accomplish this through a slight deformation at the center of the thread. This makes it nearly impossible to continue tightening down a screw and difficult to back out.


For a step by step guide please read our article on how to install key inserts. Inserts with an internal thread of 5/16’’ or larger usually have 4 locking keys. Smaller inserts will usually come with just 2 locking keys.

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