Sorry to dig up and old thread but I have also come across this, but I've come to the conclusion that because these Banebot wheels are american made, so are the grub screws, ergo, they're an imperial size. I can just about get the grub screw down and as soon as it hits any resistance the allen key just spins in the grub screw. I have no allen key that is the right size, always a little too big or a little too small.