Torque wrench head.

Many varieties, can be ratcheted, can have removable socket, spanner or wrench ends.

In the direct pawl type this extends deeply into the barrel and makes contact with the (in this case) cubic pawl.

Pawl

Can be many different shapes and sizes depending on manufacturer. A simple cube shaped one is used here. It is firmly fixed between head and cam under no load and below torque situations.

Cam

Evenly applies spring pressure to the pawl and head.

Spring

Applies (adjustable in some cases) force to the cam, pawl and head. This force is what resists the wrench clicking until the torque desired is reached.

Grip and adjustment parts

Not modelled in any detail. These parts vary widely with manufacturer and purpose of the wrench. Generally a screw pushes against a spring cylinder and serves to increase or decrease spring force depending on how much the grip is turned.

When desired torque has not been reached (or the wrench is in storage or at rest.

The spring force pushing against the cam and pawl is adequate to overcome the desire of the interior end of the head to tilt outwards and upset the pawl's orientation.

The desired torque has been reached.

Once the torque at the head is enough to overcome the spring force which is keeping the pawl in position, the pawl tilts and pushes the cam back towards the grip (in turn compressing the spring), as the internal end of the head tilts outwards and hits the body tube. This causes the audible click and noticeable tactile feedback which is characteristic of this type of wrench.