Drill Collar app is database of Ideal Drill Collar Range. When select Open Hole Size, the app will show below data: - CASING SIZE TO BE RUN, inch - IDEIAL DRILL COLLAR RANGE, inch - API DRILL COLLAR SIZES WHICH FALL IN THE IDEAL RANGE, inch The minimum size drill-collar is calculated from the Lubinski and Hock equation. Easy. Simple. Useful. Work Safe!