That's funny, the one I put one together for the hobby shop owner, it had metric hardware, on the other hand I guess that they just used 4-40 stuff instead of finding 3 or 4 mm hardware. The plane is great and requires almost no improvement, I just addad a latch and dowels instead of screws to put the hatch cover on. No tools required except for the wing bolts. Stingers are great, they fly real good and are light if built right.