Some RF connectors must be tightened with a torque wrench to the correct value specified by the manufacturer.

Often the wrench is too expensive for occasional and amateur use, but we can still *approach* the correct torque easily and with minimal cost.

Example with SMA connectors.

All we need is a wrench and a digital luggage scale.

The SMA connectors must be tightened with a torque between 0.8 and 1.1 N.m with a 5/16″ (about 8 mm) wrench, the scale can be bought on Ebay, Amazon etc.

The length of the wrench, at the centre of the nut, must be measured. This one is 110mm.

When the scale reading is 1 kg, the force applied is 9.81 N.

The mean datasheet torque value for this connector is 0.9 N.m, namely a force of 0.9N must be applied with a wrench 1m long.

With my 0.11 m wrench, the force to be applied is 0.9 / 0.11 = 8.18 N. The scale measure for 8.18 N is 8.18/9.81 = 0.83 Kg

**This force should be applied *momentarily*, as soon as you read 0.83 Kg on the scale, the connector is tightened well and the force must be removed immediately.**

The torque should be measured with the wrench in vertical position, to minimize the effect of his weight.