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.

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.

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.

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.

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