Fabricated from A-36 carbon steel, these PTP-4 A-Type variable spring supports measure 6 5/8″ OD x 19 9/16″ in length with an installed load of 596 lb. They have a spring rate of 56 lb/in., and a downward travel of 1.375″. These supports are designed to suspend from a rod that is threaded through the upper portion of the variable (see Fig. PTP-4). This particular design is generally used to keep the variable further away from the beam to avoid interference.