The TeraFlex JL / JT EcoDiesel: 1in Front Coil Spring Spacer Adjustment Kit is required with all our coil spring lift kits to properly level the front suspension on the JL Wrangler/Unlimited and JT Gladiator models with the heavier 3.0-liter EcoDiesel V6 engine. Can also be used on vehicles with gas engines as a 1in Front Coil Spring Spacer Load Level Kit to help compensate for heavier aftermarket gear such as bumpers, a winch, a larger spare tire, or weekend swag.