Drilling holes in metal fer - ARKHENO.COM- the hole drilled in sheet metal for a tapping screw should be the approximate size of the ____ ,Holes can be machined: drilling, countersinking, reaming, boring, broaching, grinding, honing, superfinishing, lapping, sizing and rolling. Drilling is used to create holes in solid metal. Holes with a diameter of more than 30 mm in solid material are drilled with two drills, i.e. drilling and reaming. Gun drills are used to drill deep holes.DIN7500 (Tap-Fix) Hole Sizes Sheet - TR FasteningsColled Rolled Steel 65 - 70%. Aluminium 70 - 80%. Thin Sheet Metals 80 - 95%. Table 1: Suggested hole sizes for Aluminium or Zinc die casting. The minimum length of thread engagement should be equal to twice the diameter of the screw. The hole diameter should provide for 65% to 75% thread engagement to ensure optimum assembly performance. Table 1.