This front shock spring is specified for TRAXXAS Slash 4x4 front dampers and is supplied as 1 pr. The 1.3mm coil length is the selection datum for expected spring behaviour when tuning the front end of the chassis.
Installation is a direct-swap in compatible front shocks: remove the shock cap and piston assembly, replace the spring, then reassemble using the intended preload and correct shock oil to restore designed damping and ride height. This part is intended for model RC suspension use only and should be handled as a tuning component.
From a setup perspective, the spring adjusts front-end stiffness and ride height. Evaluate changes one corner at a time and install matched springs in pairs to preserve symmetrical handling characteristics across the axle.