The box-inside-a-box method is
the safest way of packing your parts and its light-weight, its quick, and its re-useable. Parts can be wrapped in bubble wrap, then surrounded by styrofoam with another three inches of styrofoam between the boxes.
Breakage can and does happen when the parts aren't protected by styrofoam as shown.
After ELEVEN years, not one single part has ever been lost in shipping !!!
The inner box will carry five or six aluminum parts from a typical classic motorcycle. It will weigh around forty pounds, and it will cost $60 or less, to mail it from anywhere west of the Mississippi River. Insurance is extra. Insure your shipment for one thousand or two thousand dollars, or more, and that's the same way I'll return your parts to you when they are finished. Enclose a list of your parts inside the box and your email address so I can send you pictures when the job is done.
Save money on mailing. Don't use a carton that's too big for the parts. Both these shipments at left weigh about 38 pounds. One of these costs $32 extra (each way!) because the box is too big. The shipper is going to charge you this premium for taking up space on his truck.