Holes are through.
Would not recommend that you try. Drill press are generally high speed turning, and these are designed for hand/finger turning. You MIGHT get away with it once, but I would not consider this for a permanent installation. Go with a professional drill chuck if you're gonna go that route.
The range of collet capacities is 0-.187(0 - 3/16)
Another respondent has answered an identical question: "The range of collet capacities is 0-.187(0 - 3/16)"