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On a prototype project I am working one I have a pair of formed beam members which require a hole drilled through both sides and must be concentric to each other or reasonably well.
Since it is virtually impossible for metal to be formed to exacting angles every time when you need a hole on opposite sides you have 2 choices either lay out each side on both beams also these must be made for left and right configuration. Or to make some form of a drill jig which can be used for drilling them again remember you need left and right and to be able to drill both sides
You can not trust through drilling from one side to the other since the possibility of the formed angles being slightly askew or your drill press does not have sufficient spindle travel to preform this function with out repositioning the table.
Since this is a prototype I really didn't want to fabricate some elaborate fixture of a drill jig. I opted instead of laying out 1 hole on 1 side of 1 beam member then centered that under the spindle then before drilling the hole since trying to drill a 1 1/8" hole would mean either I would have to carefully step drill it to reduce the chance of bit wander or walking I instead clamped the beam in place then clamped 2 plates over it which were pre drilled for a 3 point contact with the contact pins in place I made a makeshift drill bushing out of a scrap piece of hydraulic cylinder rod. Positioning everything in place using the 1 1/8" drill bit as the locator I tacked the bushing to one of the plates then drilled through both plates and the beam.
Then squared the second plate on top of the drill bushing and tack welded the fixture together and used it to drill the remaining hole in the opposite side of the beam then drilled the holes in the second beam.
It is a down and dirty fixture but much closer to being able to repeatedly drill concentric holes both left and right every time
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