Keensert (Key-locking Threaded Inserts) or a Helical Insert? Which do you want to use? What’s the difference? The best place to start is right here.
These popular fasteners are used to repair damaged threads or strengthen weaker materials such as aluminum, most commonly for precision manufacturing and aerospace applications.
Let’s dig into the details.
Uses for Both Helical Wire Inserts and Key-locking Threaded Inserts
Let’s start with Helical wire and Key-locking inserts. Both are called “threaded insert” fasteners. A threaded insert is a fastener which can be inserted into an object to add a threaded hole.
A threaded insert can be used to:
- Repair a stripped hole
- Create a durable threaded hole in a soft material
- Position a thread on a material otherwise too thin to accept it
- Mold or cast threads to eliminate a machining operation
- Simplify a change from unified to metric threads
- Simplify a change from metric threads to unified
A Helical wire insert is spring-like, a precision form wire coil that looks like a slinky. It offers a permanent thread stronger and more durable that the parent, or base material. The brand name is Heli-Coil, from Emhart Teknologies.
Take a look at the advantages of these inserts. They are:
- Considerably less expensive than a key-locking insert
- Used when minimizing space is key
- Useful for creating a permanent, strong thread for softer material like aluminum or titanium
- Best suited to lower heat environments
- Used to strengthen threads against failures from tripping, corrosion, or seizing
- Used to convert threads between inch and metric sizes
It’s a misconception that these inserts are used only for thread repair in parts that need to be scrapped otherwise.
Diamond-shaped, the helically formed wire coil in this type of insert screws into a threaded hole, forming a mating internal thread for a screw or stud.
Helical wire inserts come in 2 main styles: tanged and tangless. Most widely used, tang style helical wire inserts have a prong at one end to make installation easier.
Used most often in electronic applications, newer tangless styles have no prongs to break off, retrieve, lose, or cause any damage.
Helical wire inserts are either free-running or locking, with free-running most often used for thread repair. Why? Because the free diameter of the inert is larger than when installed, generating a balanced pressure distribution between both coils and threads.
Recommended for applications that have more stress or vibration, or require constant torque, locking style inserts have a crimped turn acting as a locking mechanism. The mechanism grips the bolt or screw, preventing any loosening from vibration, as well a need for lock wiring, lock-nuts, lock washers, pellets/patches or any other thread locking devices.
You can find helical wire inserts in stainless steel and phosphorous bronze, as well as Inconel X-750 and Nitronic 60 and 90.
Keensert® Key-Locking Insert
A key-locking insert is a solid bushing style insert that is threaded on the inside and the outside with keys on the top. The brand name for these types of inserts are Keensert®, from Huck Patents, or Keysert®, from Alcoa Fastening Systems.
Advantages of a key-locking insert:
- Used when high strength and durability is required, especially in environments high in temperature and torque
- Easier to install than a helical wire insert
- Used when you don’t need to save space
- Used when whole depth is not a main consideration
- Used to distribute loads and repair or strengthen threads against failures due to stripping, seizing or corrosion
- Used in applications where fasteners may be removed and reassembled repeatedly
Often used in aerospace, common assembly applications include transmission housings, electronic equipment and suspension units.
Key-locking inserts work in this way: they’re threaded into a pre-tapped hole, and then the keys are hammered into grooves through the threads, which then permanently locks the insert into place.
The keys in this type of insert, once driven into the tapped threads, offer a mechanical lock against rotation, which is important especially in situations where the mating stud or bolt will be removed often.
Key-locking inserts come in four main styles:
- Miniature Key-locking inserts – used in electronic and aerospace applications not critical for size and strength; may be installed in sheet material as thin as 1/16.″
- Thinwall inserts – excellent for tight spaces where less pull-out strength is required; have smaller external threads than standard heavy-duty inserts.
- Heavy Duty inserts – suitable for almost all applications, these inserts feature a thick, heavy-duty thread wall
- Extra-heavy duty inserts – used for oversized and overly worn holes
Key-locking inserts can be either internally self-locking or standard non-locking, which is used for most common applications.
Inserts with the internal self-locking feature securely lock a bolt entered in the insert in just a few turns. only a few turns. Internal self-locking types will maintain enough torque to prevent the bolt from vibrating out even after repeated installations and removals.
You can find key-locking inserts in carbon steel, stainless steel, and alloy.
Which Insert Should You Choose?
So, as discussed, you’ll find there are three main differences between Key-locking inserts and Helical wire inserts:
- Strength – key-locking inserts are stronger
- Installation Ease – key-locking inserts are easier to install
- Price Point – helical wire inserts are less expensive than key-locking types
Here’s some facts worth noting. When your installation is in a high vibration, high heat situation, key-locking inserts are the best choice, assuming space saving is not an issue, and the hole depth is limited.
But, when you want to reduce cost or minimize space, helical wire inserts are the best suited to these applications.
They’re most suitable for lower heat and lower torque environments, and are especially useful to provide permanent strong threads in softer materials like aluminum, titanium and magnesium alloys.
If you’re looking for a reliable, high-quality manufacturer of keenerts and helical inserts, and ready to find more information about which type of insert is right for you, reach out to MF Supply. They are a trusted supplier of Threaded Inserts & Helical Wire Inserts to OEMs & Manufacturers and have a huge inventory including major brands and equivalents to Alcoa, Camloc, Fairchild, Kaynar, Microdot, Tridair and more. As their motto says: They have the right screw for you!