ClearBags.com sells these clear boxes perfect for storing loose 1/64-scale diecast vehicles, such as Hot Wheels or Matchbox.
This 1 1/2″ x 1 1/2″ x 3″ box should hold most Hot Wheels cars nicely, protecting them from scratches and dust. These also come with clear stickers designed to close/seal the box.
There is also a slightly larger 1 1/2″ x 1 1/2″ by 4″ version of the box for those slightly larger diecast vehicles.
