Holley Pump Nozzles

The tube type can't be re-drilled. They have a nozzle at the end of the tube that tapers down from the diameter of the tube. Drilling the tube destroys the nozzle, and changes how the whole thing flows. It's not just the final diameter that matters, but the shape of the passage too.

The straight kind can be redrilled. They're like $13 a pair though, so I don't usually bother. Maybe my trust is misplaced, but I have to think that the factory is probably better at getting that diameter down to within .001" accuracy than I am.