"This Reliable UNDERSLUNG Trailer Axle is quality built to meet your trailering needs. Axle Tube Type Round, Weight Capacity lbs. 3,500, Axle Outside Diameter in. 2 3/8, Inner Bearing Size in. 1.378, Outer Bearing Size in. 1 1/16, Spring Centers Length in. 54, Overall Length in. 71 1/4, Brakes Included No, Axle Drop in. Straight, Hubs Included No, Springs Included No, Spring Seats Welded, Seal Size in. 1.719, Track Length in. 66. 71.25in. overall length 3500 lb. capacity 54in. spring center 2.375in. tube dia. with camber Shackle set not included"
The track length is the distance from the hub face on the right side of the trailer axle to the hub face of the left side of the trailer axle. If the rims of the tire assemblies are centered it can be measured from the center of the tire on the right to the center of the tire on the left.