The axle assembly started life under the front end of a truck before seeing duty under a trailer.
Chains are wrapped around the log and pass through two conveniently located triangular openings in the axle assembly (where the control arms are welded to the main axle body to keep the wheels aligned). The chain ends are then fixed to the tractor so the pulling force also securely clamps the log to the axle.
Here's Dad pausing on the driveway to change to a higher gear.
And we're off to the mill.