From the Manufacturer
Drivehead has adjustable locking head for various lengths of stretching. Stretcher adjusts from 35 in. to 22 ft. Knob on head allows easy adjustment of power pins for various carpet thicknesses. The driving head has an adjustment for partial carpet stretches. Comes complete with power head, 4 extension tubes in a tough, durable case with heavy-duty hinges, handle and double latches.