Connector torque

Updated February 16, 2007

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The first information on this page was contributed by Ruth, a true expert in the subject of coax connectors! Further info was later contributed by Stephen T. Morley.

This question was sent in: what is the correct torque for different connectors, and in what documents give this information?

The MIL specs for connectors usually specify a "recommended mating torque" in the beginning of each slash sheet. Many connector manufacturers specify that value in the general specification pages for each connector series and I have not seen many inconsistencies among the various manufacturer's. The only place you have to watch out is when there are brass versions of traditionally stainless steel products as in the SMA and SSMA styles. Due to the nature of the design if you torque a brass SMA to the specified torque of 7-10 in-lbs and the male housing is of the thin wall variety you can get a roll over condition. Most manufacturers will specify the brass connectors at a lower torque value... or only supply a thick wall male. Here are some of the more popular interfaces and the mating torque that I have always specified.

SMA (stainless steel) 7-10 in-lbs
SMA (brass) 3-5 in-lbs
SSMA (stainless steel) 7-8 in-lbs
SMM (stainless steel) 2-3 in-lbs
SMC (brass) 3-5 in-lbs
Type N 12-15 in-lbs
TNC 12-15 in-lbs
SC 12-15 in-lbs

By the way, to convert from inch-pounds to Newton-meters, multiply inch-pounds by 0.113.

It is important to note that some interfaces like the Type N and TNC which can have a slotted or solid male housing must be watched carefully. The slotted housing is specified to a lower frequency and is much more forgiving than a solid housing. If a technician were to tighten a slotted type connector with his "calibrated" fingers it would most likely be OK and not particularly affect the performance. A solid housing however requires a closer watch on the torque therefore a torque wrench is highly recommended.

This info was sent to us by Mr. Morley after we posted the page, for the most part it agrees with Ruth's numbers:

Here are torque recommendations for coax connector coupling nuts compiled by Stephen Morley:

Here are torque recommendations for coaxial connector jamb nuts compiled by Stephen Morley:

Here's a bonus! Stephen Morley sent in this King's English/American English translation sheet for connectors, check it out!