The Watts linkage can be either “axle mounted” or “chassis mounted”. This refers to the location of the Watts lever pivot axis.

Axle mounted Watts link pivot.

There are four chassis mounting points, one for each trailing arm, one for each Watts link.

There are four axle mounting points, one for each trailing arm, and two for the Watts pivot, one of which is reference point to determine the pivot axis.

Chassis mounted Watts link pivot.

There four chassis mounting points, one for each trailing arm, and two for the Watts pivot, one of which is reference point to determine the pivot axis.

There are four chassis mounting points, one for each trailing arm, one for each Watts link.

The two trailing arm mountings can be a single point.