The arm is made of 2x4 wood. It consists of two parts, the main arm plus a hinged weight support.

Measurements:

From pivot to end 27"
From pivot to weight hinge: 16"
From weight hinge to weight axle 7"

The main hinge is a pipe section with some short pieces of PVC pipe on it to keep the arm centered. The extra length makes good handles for moving it around.