The key to a beautiful lawn is aeration. Without proper aeration to prevent compaction, grass can't spread its roots into the soil, and thatch will grow out of control. A core aerator will pull out small cores of soil, and allow the ground to decompress to fill in the holes. The holes also allow grass seed and fertilizer to penetrate into the soil and work properly. 16 tines are installed per wheel, the tines will alternate between 2.5" and 4" to allow maximum penetration for awesome aeration, and shallow holes for grass seeds. The Everything Attachments lawn aerators have a 2" main axle with greasable wheels and outside bearings to greatly reduce wear on the axle.