Insert Retention: Tangless® vs. Tanged Inserts - Article 0599

KATO Technical Bulletin 0200-1a

We have recently learned that our major competitor is widely distributing a test report that purports to show that Tangless® CoilThread® Inserts are far inferior to our competitor’s tanged versions relative to retention in the tapped holes. We disagree; and it’s time we set the record straight! It is very easy to conduct a test where the results come out in the form that represents your product in the best light. This is why pharmaceutical companies conduct double blind studies. Neither the patients nor the doctors know what the patients are taking. This allows the drug manufacturer to review objective, unbiased and uninfluenced results to reach their conclusions.

Understanding the motivation behind our competitor’s test report requires a brief history lesson on the development of the Tangless® Insert product line. One must also keep in mind the superior aspects of the Tangless design covered by 8 patents. The Tangless® design was a joint R & D effort between Kato and Fairchild Aerospace Fastener Division in the mid to late 1980’s. The major design parameters that were established at the onset of the project were that Tangless® Inserts had to be equal in form, fit, function, and performance to tanged inserts. As we had over 2 decades of experience manufacturing tanged inserts, we were well versed in the performance criteria.

Regarding insert retention in the tapped holes: both tanged and Tangless® inserts employ the same retention principle. The inserts in the free state are larger in diameter than the tapped holes. The inserting tool reduces the diameter of the insert during installation. Once released from the tool, the insert springs outward anchoring it in the tapped hole.

As Tangless® inserts are identical to tanged inserts in every way except for their methods of installation and removal, and they have the exact same procurement specification, MIL-I-8846, there is absolutely no difference in their retention characteristics when subjected to shock, vibration, fatigue, torque or any other conditions that would cause the inserts to move.

In 1991, Tangless® inserts were tested by an independent test lab, United States Testing Co., as part of the process for publication of NAS1130.The inserts were subjected to the same military and commercial test requirements that cover tanged inserts. The inserts met or exceeded all applicable standards.

Currently, the only test that is required that gives some indication of insert retention is the 15 cycle locking torque test performed on locking tanged and Tangless® inserts. The insert cannot move from its installed position throughout the entire test. If insert movement occurs, the insert fails the test. Every manufactured lot of Kato inserts (Tanged or Tangless®) receives this test.

As we previously stated, it is relatively easy to control the parameters of a test, such that the outcome of the test is reported in a very favorable light. It is just as easy to leave out the very positive aspects of one’s product in order to publicize some purported advantages of another.

Here is an example: Did our competitor mention that Tangless® inserts have chamfered ends and notch angles whose specific design function when used with KATO® patented tools is to make the inserts easier to install and remove? Of course they did not! In fact, they had to cut a notch in the top of their insert in order to create a place for their removal tool to grab. It is almost impossible to remove a tanged insert without damaging the parent material, which typically is a soft material like aluminum. These factors alone could easily explain the disparity in the torque values as measured by our competitor. Tangless® inserts are designed to be removed with no damage whatsoever to the parent material.

Another important oversight by our competitor:

The notch on Tangless® inserts is specifically designed to allow the removal tool to grab it and easily remove the insert. What is the configuration of the notch added to their tanged insert? This notch could be easily cut in a profile that causes the removal tool to push the top coil outward into the parent material, thus making the inert difficult to remove, but giving the false appearance of greater insert retention from the measured torque. We’re not saying they did this – just that it could very easily be done.

There is no mention of the comparative free outside diameters of the tested inserts. When doing tests, one must compare apples to apples. Both tanged and Tangless® inserts are manufactured at the lower end of the tolerance for free OD as specified in the military and aerospace standards, in order to make them easier to install. However, the tolerance range is quite broad. If an insert were manufactured at the maximum end of the tolerance, it would be very difficult to install, but it would have the best retention characteristics. We noticed that there is no mention of this in our competitor’s report. However, this is an important point that should not be overlooked.

You may find it interesting to note that it was our same major competitor who approximately one year after the publication of NAS1130, requested that vibration testing be removed from the procurement spec for tanged and Tangless® inserts; MIL-I-8846. This request was approved. For the record, Tangless® inserts passed the required vibration tests that were at that time in effect, as part of the NAS1130 approval process. 

One could easily speculate that our competitor's desire to eliminate vibration testing resulted from either the rigorous and time-consuming nature of these tests, or the difficulty of helical coil inserts (tanged and Tangless) passing these test in general. We agree.

The single most critical factor in the design of a bolted assembly to keep it from loosening is quite obvious and elementary to even the most junior of engineers. This factor is the loading along the axis of the male fastener created by the tightening torque on the bolt or screw that allows the assembly to maintain clamp load (not loosen) under vibration. The causes for a bolted assembly remaining tight or loosening when subjected to vibration are absolutely NOT related to the use of a tanged vs. a Tangless® insert! – And, these causes are particularly NOT related to the test method used in our competitor’s report! To the best of our knowledge, there are no applications of helical coil inserts on this planet that duplicate the test setup used by our competitor!

In conclusion, we believe that we have clearly shown that it is quite easy to create specific circumstances that depict the positive aspects of one’s product while disparaging the superior design features of another. If our competitors feel that our product is as bad as they contend, why are they so eager and adamant to license our technology? We at KATO® take unfounded, disparaging and detrimental remarks to our products and company very seriously. We encourage you to discuss with us directly any particular concerns that you may have with our fasteners, and not simply rely on what a competitor to Kato Fastening Systems tells you, or submits in a misleading test report.