The Economy Slat Mill  The Economy mill has the same aluminum frame and composite plastic track belt as the Basic HD Mill. It is free spinning and has black side walls.  The tether risers are fully adjustable for the length of the mill and up and down.  It is a basic no frills mill that runs as smooth and quiet as any other mill on the market. All accessories except for the Accubrake can be added.  It is available in 5 standard sizes. It is also available as a kit. The Basic HD is the same mill  but with heavy duty 1.25" aluminum axles and bearings. The basic HD can accept all accessories. About Size