The center bearing is easily adjusted by inserting the shaft into the bearing and turning into position. This is a good design to ensure the shaft doesn't bind if the "feet" aren't on a perfectly flat surface when tightening. The inside diameter of the hole is exactly 5/8 inch. A centerless ground 5/8" precision O1 tool steel boring bar might not easily slip through the hole, but could likely be driven through. So I used a 5/8" coated rod from a hardware store to make it easier to slide.