<Small dia. hammered punches, called "arch punches" (try General Tool Co.) <might be good. Any competent machinist should be able to convert a That works as well. Small punches (I measured the hole at 0.096 +-.001) are easily gotten. But to do it correctly you have to position the hole reasonably accurately. For that you need an indexer, so that the index hole to sector 1 and the remaing nine fall at the correct places. An old drive mostly stripped would do for that with the flywheel marked using a known disk with the envelope removed. Perfect use for a dead 5.25" drive of any type though some may provide better mounting and access. The head, track00 sensor, index sendor, motor and logic can be removed s all that is needed is the spindle and door clamp assembly. The anvil for the punch can be mounted in the drive and the clamp closed such that index hole is at the anvil position in the index mark on the flywheel. With the door closed the flywheel can then be rotated to each position and the hole then punched. The correct position on the perimeter of the flywheel can be notched at the 11(for 10 sector, 17 for 16 sector) positions and a spring steel detent made. A precision of 1 degree is easy to achieve and would insure good operation. Once done, converting 360k soft sector media to 10 sector would be easy and fast. Allison