Adjustable Wheel Cribs are a two-piece version of your standard Wheel Cribs. Each crib comes as a stacked assembly of two interlocking pieces of equal height. Their design allows the vehicle to be lifted in incremental heights that provide clearance for a jack and a spacer. Each set supports 3,000 pounds, yet each crib weighs only 7-10 pounds! They can hold tires up to 12" wide with diameters from 25" to 30". You can use one set as either two 8"/10"/12" cribs, or four 4"/5"/6" cribs when the set is split (heights depend on which model you purchase).