Torque Test Explained

KATO Fastening Systems certifies Tangless® and tanged self-locking CoilThread® screw thread inserts to NAS1130 and NASM21209 respectively. The 15-cycle torque test is a particular test outlined across multiple National Aerospace Specifications. The thread preparation of the aluminum test block is outlined in NASM33537. The insert dimensions are detailed in NAS1130 and/or NASM21209. Finally, the test bolt requirements and torque measurement procedure are explained in NASM8846. For reference, the coverage of the specifications mentioned in this article can be found on our website.

Thread Preparation Requirements

NASM8846 is the procurement specification for all of KATO CoilThread inserts. In this specification, the thread preparation requirements (found in NASM33537) are listed.

The internal threads must be:

Bolt Properties

Stated in NASM8846, the bolt must be:

Torque Measurement Procedure

Using internal and external threads outline in the above sections, measuring the prevailing torque of the installed insert should be done per the following procedure:

So, the maximum locking (prevailing) torque going into the bolt is measured, as is the minimum torque required to remove the bolt. Semantically speaking, the torque value table measures the maximum torque for installation, and the minimum torque for removal. Not, a range for installation. The minimum breakaway torque is the important number for design engineers.

Differing Torque Values

When requested by the customer, KATO supplies the 15-cycle torque test performed at the manufacturing facility. However, it is always advised that customer perform their own torque test to verify they get the desired values in their application. It is unlikely the customer will get the exact torque values measured at the manufacturing facility. Cadmium plated bolts are rarely used in the field anymore, and different frictional coefficients can yield different torque results. There should be minimal difference between measured torque values assuming galling does not occur. Soft, uncoated stainless steel bolts are very popular in the aerospace industry, but are not allowed for testing per NASM8846. Stainless steel bolts tend to gall. For galling protection, please see our technical article.

If you have any questions, please contact us.