What is Connector Torque?

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- everything RF

Aug 14, 2020


Connector torque is the amount of force required to make a proper connection between two threaded coaxial connectors. Connections in most RF & Microwave systems are made using coaxial connectors – these might by connecting two systems together with connectors soldered on a PCB, connecting a device to a coaxial cable or connecting a coaxial cable to test equipment.

To ensure a good RF connection, one must make sure that the connector interfaces are fully engaged during installation and remain engaged during use. To do so the right level of torque must be applied when making the connection. 

The system designer, and those responsible for system installation and maintenance, use different connector types. In the production line, certain tests need a specified coupling torque to be used during the measurement process. Proper torquing of threaded RF coaxial connectors is essential for reliable, maximum performance interfaces. It not only ensures that the initial contact is proper, it also protects against changes in geometry while handling and operational environment conditions.

The recommended torque level for threaded coaxial connectors is determined by the size of the connector and the materials from which it is made. Most connector types have recommended torque levels that should be applied in order to provide a good connection. The application of insufficient torque will result in a poor or unstable connection while an over-torque will damage the mating surfaces and coupling mechanisms.

Recommend Torque Values for Coaxial Connectors

Connector TypeRecommended Torque
7/16 DIN221 - 265 in-lbs
Type F
15 in-lbs
Type N (Stainless Steel)12 - 15 in-lbs
Type N (Brass)6.2 - 9.7 in-lbs
TNC (Stainless Steel)12 - 15 in-lbs
TNC (Brass)4.1 - 6.1 in-lbs
SMA (Stainless Steel)7 - 10 in-lbs
SMA (Brass)3 - 5 in-lbs
SSMA3 - 5 in-lbs
OSMM2 in-lbs
SMC1.9 - 3.1 in-lbs
1 mm7 - 10 in-lbs
1.85 mm8 lb-in
2.9 mm7 - 10 in-lbs
2.4 mm4 - 6 in-lbs
3.5 mm8 in-lbs
4.1/9.589 in-lbs
4.3/1044 in-lbs

Note: These are recommended torque requirements compiled from multiple sources

The required connector torque depends on the material, size and operational frequency of the connector. Connectors made from brass have lower torque requirements than the connectors made of stainless steel.

Small diameter connectors, which include the SMA, 2.9 and 2.4 mm types, are used in high frequency applications. They are almost always made of stainless steel and rely on surface mating.

Mid-size connectors, which include N Type and TNC, are available in more variations to address specific needs. Standard TNC and N connectors are designed for use below 11 GHz and are made of brass, which limits the installation torque that can be applied without damaging the interface and coupling components. Precision stainless steel TNC connectors have been developed to provide reliable connections under extreme conditions and to extend the effective operating frequency range to 18 GHz. The requirements for these connectors are addressed in the MIL-T-81490 and MIL-C87104 specifications.

The installation torque level for precision connectors is increased from the standard connector value of 10 to 13 inch-pounds to 20 to 26 inch-pounds. This added torque makes them more suitable for airframe and other high vibration applications. Large connectors are designed to be installed with high torque levels, thus assuring a secure connection under all conditions. The 7-16 DIN is a connector widely used in the telecommunications industry, particularly where low passive intermodulation or high power handling is required. It is designed to be installed with a torque of 220 to 300 inch-pounds, which is a full order of magnitude greater than for the type N or TNC.

To ensure a secure connection is made, Torque Wrenches can be used. Torque Wrenches are available for various connector types like SMA, Type-N etc. and can be used to secure threaded coaxial connections with the right amount of torque to ensure that they do not become loose. everything RF has created a tool to help users find Torque Wrenches for Coaxial connectors. Click here to find Torque Wrenches for coaxial connectors.