Sightron Target Knob re-set

[Harold M]

Hopefully someone has the answer. I would like to re-set the knobs on my SIII to zero. The instruction says what size allen key to use - either a 1.5 mm or the next size up in 64ths. I tried every metric and inch key and bit I have, one being the 1.5 mm, and nothing works. These are the knobs with the 3 grub screws around the circumference of the knob, not the ones with the torx through the center of the top. Anyone know what to do?