They relocate the rear leaf spring inboard to accommodate 335 tires ( with a section of 13.5″ ) on a F-Body/X-Body. The shackle offset is 1-3/4″. Use along with our other mini-tub components to complete your project. Kit includes 4 offset shackles and Grade 8 fasteners. This is the ORIGINAL billet aluminum offset shackle! The Detroit Speed shackle is designed for maximum suspension travel. There are hundreds of our shackles on the road and track with proven performance. Do not accept any imitation!