Making Good Connections

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Good connections require a skilled operator. The most common cause of measurement error is bad connections. The following procedures illustrate how to make good connections.

Making a Connection

  1. Wear a grounded wrist strap having a 1 MW series resistor.

  2. Inspect, clean, and gauge connectors. All connectors must be undamaged, clean, and within mechanical specification.

  3. Carefully align center axis of both devices. Push the connectors straight together so they can engage smoothly. The male center conductor pin must slip concentrically into the contact finger of the female connector.

  1. CRITICAL: Rotate only the connector nut - NOT THE DEVICE OR CONNECTOR BODY - until finger-tight, being careful not to cross the threads. Damage to both connectors will occur if the male center pin is allowed to rotate in the female contact fingers.


  1. Use a torque wrench to make final connection. Tighten until the "break" point of the torque wrench is reached. Do not push beyond initial break point. Use additional wrench, if needed, to prevent device body from turning.

Separating a Connection

  1. Support the devices to avoid any twisting, rocking or bending force on either connector.

  2. Use an open-end wrench to prevent the device body from turning.

  3. Use another open-end wrench to loosen the connector nut.

  4. Complete the disconnection by hand, turning only the connector nut.

  5. Pull the connectors straight apart.

Using a Torque Wrench

Proper torque on the connector improves measurement repeatability and extends connector life. The tightening torque on connectors has a significant effect on measurements at mm-wave frequencies. Repeatable measurements require consistent torque on all the connections in a setup. A torque wrench avoids damage due to over-tightening and helps connectors achieve their rated lifetimes.

  1. Make sure torque wrench is set to the correct torque setting.

  2. Position torque wrench, and a second wrench to hold the device or cable, within 90° of each other before applying force. Make sure to support the devices to avoid putting stress on the connectors.







  1. Hold torque wrench lightly at the end of handle. Then apply force perpendicular to the torque wrench handle. Tighten until the "break" point of the torque wrench is reached. Do not push beyond initial break point.

Torque Settings


Torque Setting

Wrench Part Number

1.0 mm

4 in–lb (45 N–cm)


1.85 mm

8 in–lb (90 N-cm)


2.4 mm

8 in–lb (90 N-cm)


NMD 2.4 mm

8 in–lb (90 N-cm)


2.92 mm

8 in–lb (90 N-cm)


3.5 mm

8 in–lb (90 N-cm)


NMD 3.5 mm

8 in–lb (90 N-cm)



5 in–lb (56 N-cm)


Learn more about NMD connectors.

An SMA torque wrench is NOT structurally identical to a 3.5 mm torque wrench. They have similar shape but different coupling torque.

To connect an SMA male to a 3.5 mm female connector, use an SMA torque wrench.

To connect a 3.5 mm male connector to a SMA female connector, use a 3.5 mm torque wrench.