From the Manufacturer:
This is a single rear poly coil spacer to help correct for vehicle lean once a vehicle has been lifted, if a lean exists.  It is 15mm (0.6") thick.  This will add the same amount of lift as its thickness to help level up the vehicle.  These CANNOT be stacked, only 1 can be used per coil spring. These will suit all rear coil springs that use the factory top rubber coil spring isolator, for these vehicles: 4Runner - 2003 to 2019 (4th and 5th Gen) FJ Cruiser - all years Lexus GX470 and GX460 - all years Prado 120 and 150 - all years
This coil spacer is also ideal for vehicles with KDSS, as offset height rear coils, or a spacer on top of one side if even height coils are used, is recommended. Remember: New Toyota vehicles come with a 1/4" to 1/2" lean from the factory, so anything within that range is considered "OK".