After a few miles of off-road riding, the screws in the left pedal of my Downtube IX FS came loose and were lost. I didn't see any mention of the screw size on the forums here, so I thought I'd post what worked for me should someone need this information in the future.

I was able to replace the two screws with 6-32 (about .1" diameter) machine screws. I used a Dremel to cut them down to 3/4". At that height -- and with a flat head -- they were flush with the pedal.