MRR110. Carbide Tipped Miniature Corner Rounding 3/16 Radius x 9/16 Dia x 3/8 x 1/4 Inch Shank with Mini 3/16 Dia Lower Ball Bearing. We’ve created the smallest guide bearings in the industry! If you’ve often wanted to trim and shape small details in tight corners, but were disappointed by the scoring and burning left behind by solid pilot bits, we’ve got what you’ve been looking for: eight of the most commonly used profiles in miniature sizes – complete with tiny miniature ball bearing guides.