DMBS-MB60 Deltronic Metric Micro Ball Set 1-20mmChrome Alloy Steel Micro Balls, + . 0001" Diameter, . 000,025" Sphericity Common uses for these Steel Micro Balls Allows you to check micrometers at exact spots for wear. Check wall thicknesses from inside curve to flat outside. Check the depth of valve seats, ways and slots. Maintain Depth of Center Drill in turning and grinding, where shoulder locations to each other or to a common end are held to a close tolerance (. 001"). Features include 1 20mm