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On my magnum block I started with a 1/4 inch bit then went to a 9/32 then 5/16.
On my 340 the factory, step drilled it with a 5/16- 1/4. The last inch or two was all that needed drilled into the galley.
I did learn to stick a long screw driver or bar into the galley to stop me from drilling into the back wall of the galley.
procharged don't junk that block yet.
I used a battery powered drill at low speed and drilled it dry.
