8mm drill and you're good to go. Did it my '83 Trek 600. No issues whatsoever.
I drilled the fork in the back side only. The rear brake bridge is more difficult to do it that way, so I just drilled the whole way through. The rear brake does so little work in overall braking that I'm not worried about any minor movement, but it doesn't move anyway.
edit: maybe I should learn to read
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72 Frejus (for sale), Holdsworth Record (for sale), special CNC & Gitane Interclub / 74 Italvega NR (for sale) / c80 French / 82 Raleigh Intl MkII f&f (for sale)/ 83 Trek 620 (for sale)/ 84 Bruce Gordon Chinook (for sale)/ 85 Ron Cooper / 87 Centurion IM MV (for sale) / 03 Casati Dardo / 08 BF IRO / 09 Dogma FPX / 09 Giant TCX0 / 10 Vassago Fisticuff
Last edited by Ex Pres; 05-01-09 at 09:53 PM.