Keensert® Buyer’s Guide

Keensert® Buyer’s Guide

5 Things You Need to Know

If you are a precision manufacturer working in high-torque and high-temperature situations, you might already be familiar with Keensert® key-locking inserts.  Common uses include thread repair applications or to provide thread durability in situations such as aerospace assemblies, electronic equipment and suspension units.

But, what exactly are they and what should you know before buying them? We’d like to help you out with this quick buyer’s guide.

  1. What is a Keensert®?

A Keensert® is a solid bushing style insert that is threaded on both the inside and the outside, and has wedges or “keys” attached at the top. They are generically called key-locking inserts, and are used to distribute loads and repair or strengthen threads against failures due to stripping, seizing or corrosion.

Although the name Keensert® is often used generically (like Band-Aid® or Kleenex®), Keensert®  is the registered trademark of Huck Patents (its close cousin, the Keysert® is a registered trademark of Alcoa Fastening Systems.).

Before you shop, check to see if the bill of materials specifically calls out Huck or Alcoa brand as the Keensert®  manufacturer. If no specific manufacturer’s name is listed, then you can typically use an alternative like Rock Solid brand, a generic equivalent or cross to a MIL-SPEC part.  This becomes important due to price and availability of the brand name parts.

  1. What materials and sizes are available?

Keenserts are available off the shelf in 303 stainless steel or carbon steel. Standard diameters are: American #6-32 to 1 ½” and Metric  M4 to M24. Other diameters (starting at 2-56 and M2) and materials (including 316 stainless steel, and alloys 4140 and A286) are available for special order and usually involve a lead time.

  1. What information do I need for ordering?

To order, you’ll need the manufacturer’s part number or the internal and external thread and material. Alternatively, key-locking inserts often show up under their MIL-SPEC numbers, which can often be crossed to commercial equivalents. Common MIL-SPEC numbers include: MS51830, MS51831, MS51832, NAS1394, NAS1395, NA0146, NA0147, NA0148, NA0149, NA150, and NA0151.

  1. Do I need to buy special installation tools?

When purchasing key-locking inserts, check with your production department to make sure you have the tools you need to properly install inserts. You can buy kits that include a tap, drill, and installation tool.

  1. What level of certification is required?

Generally, a Certificate of Conformance or a COC is sufficient. Full certification with material certs and test reports are often available for a fee.

In summary, in order to have the most efficient Keensert shopping/buying experience, be prepared with the following information before you shop:  Do you need the Alcoa or Huck brand product or can you use a generic or MIL-SPEC alternative?  Make sure to have the manufacturer’s part number, MIL-SPEC part number or the internal/external thread and material.  Do you need an installation tool? Finally, check to see if you require a standard COC or full certs.

For more information about MF Supply contact:

Robin Lieberman, President


What the heck is a Keensert® Key-locking insert?



What the heck is a Keensert® Key-locking insert?


  Key-locking insert 


We close out the first quarter of 2013 by introducing you to the Keensert Key-locking insert. Like its relative, the Helical wire insert, (see January 2013), the Key-locking insert was originally designed to repair parts with damaged threads.

What is a Keensert Key-locking insert?

The Key-locking threaded insert is a solid bushing style insert that is threaded on both the inside and the outside, and has wedges or “keys” attached to the top of the insert. Keensert® is the registered trademark for one of the most popular brand names for this part and is used commonly to describe this insert.

Who uses Key-locking inserts?

Generally, Key-locking inserts are used to distribute loads and strengthen or repair threads against failures due to stripping, seizing or corrosion.  Key-locking inserts are commonly used in high torque and high temperature situations, and in applications where fasteners may be repeatedly removed and reassembled.

Typical applications are transmission housings, electronic equipment and suspension units. Key-locking inserts are common in the aerospace industry.

Why use a Key-locking insert vs. a Helical wire insert?

There are three main differences between Key-locking inserts and Helical Wire Inserts: Key-locking inserts are stronger than helical wire inserts, they are easier to install than helicals, and they are more expensive!

In heavy wear, high vibration and high heat situations where saving space is not a concern and hole depth is limited, Key-locking inserts are the best bet. Their “keys”, which are driven down into the tapped threads, provide a mechanical lock against rotation, especially when the mating stud or bolt will be removed frequently.

When reducing costs and minimizing space are priorities, helical wire inserts are the way to go. They are particularly useful for creating permanent strong threads in softer materials such as aluminum, titanium and magnesium alloys, and are best suited to lower heat and lower torque environments.

What styles are available?

Key-locking inserts come in four main styles: Miniature, Thin Wall, Heavy Duty Wall (general purpose) and Extra Heavy Duty. Inserts can be locking or non-locking.

Miniature Key-locking inserts are used in electronic and aerospace applications where size and strength are critical. These inserts may be installed in sheet material as thin as 1/16″.

Thinwall  inserts have smaller external threads than standard heavy-duty inserts and are ideal for tight spaces where less pull-out strength is acceptable.

General-purpose Heavy Duty inserts have a thick, heavy-duty thread wall, suitable for most applications.

Extra-heavy duty inserts are used in oversized and overly worn holes.

Installation is 5 easy steps!

1) Drill with a standard tap drill and countersink with a standard 82° – 100° countersink (90° for Miniature Inserts). Note: Drill is oversize see charts for proper dimensions.

2) Tap new threads with a standard tap.

3) Screw in the insert until it is .010-.030 (.005-.015 for Miniature Inserts) below the surface. Keys locate the proper depth.

4) Drive keys down with several hammer taps on the proper installation tool.

5) You are done!  


Considerations for selecting and using Key-locking inserts.

  • Inserts often show up under their Mil-spec numbers, which can be crossed to commercial equivalents. Some common Mil-spec series for Key-locking inserts include: MS5180, MS51831, MS51832, NAS1394, NAS1395, NA0146, NA0147, NA0148, NA0149, NA150, NA0151.
  • As discussed, Key-locking inserts are often referred to by their brand names, which can often be substituted by generic equivalents. Popular brands include: Alcoa, Fairchild, Keensert and Tridair.
  • Materials available include Carbon steel, Stainless Steel, Alloy 4140 and A286.
  • Diameters available: American – #6   to   1 1/2 ” and Metric – M4   to   M24
Key-locking inserts at MF SupplyWe offer:  

  • The full range of commercial and mil-spec parts
  • Products kits including single and multiple sizes
  • We are authorized distributors for Chrislynn and E-Z Lok

For more detailed information on Key-locking insert, visit us at

And if you don’t see it listed, as always, ask us. Finding the right screw for you is our tag line after all!