These are the pulleys that bolt to the Harmonic Damper and drive the water pump, alternator and power steering. Commonly known as "Crank" or "Drive" pulleys. When we are describing the dimensions of our pulleys, we will refer to offset and groove number. The offset of the pulley grooves is measured with the pulley laying on its back. We measure the distance from the rear flange of the pulley (where it bolts up to the damper) to the center of the belt groove. When we refer to groove numbers, groove 1 would be the groove closest to the damper, groove 2 would be the next farthest, and so on.