And there are some folks who advocate a 9/32" drill (0.281), because there is more clearance. They usually recommend using a Polyurethane glue because it will expand to fill the larger gap.
The real advantage to using the larger drill and Poly glue is that the glue expands into the gap and retains a degree of resiliency that allows for wood movement. This will reduce or eliminate the cracking that is a problem with woods like Ebony.
Some folks also use a little water inside the wood with the Poly glue, and the extra clearance will allow for some wood expansion and the tube will still fit in the hole.
For what it's worth, I have never liked the 7mm bit because the hole is too tight a fit with the tube for me. The "J" bits are too difficult to find. The 9/32" is available everywhere when I need a new one. Even Home Depot has a 9/32" drill. I use the 9/32" drill on most 7mm pens with CA glue, epoxy, and Poly glue without water, all without any problems. I reserve the smaller diameter drills for those special cases where I want a tighter fit between wood and tube.
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