All Arrowcraft adaptors are made from steel.  There is no aluminum in any adaptor.  Arrowcraft designed the adaptors to mount directly to your existing axle stud requiring no modifications on your part.  Simply remove your single wheel and tire and mount the conversion hub in the single wheels place.  The conversion hub will give you the proper spacing and convert the vehicle from a stud piloted to a hub piloted mounting for dual wheels.  The adapters are approximately 3-4" thick depending on vehicle type with 5/8" studs.  The conversion kit will come with all the pieces need to complete the job, wheel packages are also available.  100% precision machined from solid steel billets, absolutely NO aluminum.