Hot rolled material is neither round or straight, so a piece of brazing rod has been clamped between the chuck jaws and the work piece. This old machining technique allows the outer end of the stock to align with the axis of the machine without binding or fighting the jaws of the lathe chuck. Slippage will not be a problem as this is not a heavy machining situation: the cuts to be taken are relatively light. Less than 1/4 inch has to be removed from the shaft to achieve finished size.

Photo by Bill Liebman.