Originally Posted by
Retro Grouch
The trick on the rear is that you don't have enough space to get your drill in there. My trick is to clamp the drill bit in my vice grips and rotate it by hand. You don't have to drill out very much metal so it's not as bad of a job as it sounds.
You can drill all the way through and then use a shoulder washer to cap the rear side. Cinelli actually made their bridges that way and supplied two shoulder washers. Install one on the rear if you use a recessed bolt; install both if you use a standard bolt:
Here's what I use when I need to counterbore a hole for recessed bolts:
