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Drill Size Factors

  • Tapped holes deeper than 1.5 diameters often call for a larger tap drill.
  • Blind holes often require larger tap drills to reduce loads on the tap caused by chip buildup in the hole.
  • Materials that tend to gall when tapped or when fasteners are installed should have larger drilled holes.
  • Under tapping pressure, soft materials tend to extrude and enter the root area, necessiating a larger drilled hole.
  • Materials that don't readily dissipate heat, should have larger holes to reduce the tooth contact area and minimize heat build up.
  • When making threads with high helix angles using a larger tap drill will help reduce tap breakage.