The Tap & Die Co (established 1978)

  Axis: The longitudinal centre-line of the drill
  Angles:
   Helix Angle The angle between the leading edge of the land and the drill axis. Most drills have this Normal Spiral or Helix
   Slow Spiral or Helix Angle A helix angle which is smaller in angular value (ie. number of degrees) than normal helix angle, thereby lengthening the lead of helix. Lead longer than normal
   Quick Spiral or Helix Angle A helix angle which is larger in angular value (ie. number of degrees) than normal helix angle, thereby shortening the lead of helix. Lead shorter than normal
   Rake Angle The angle between the face and a line parallel to the drill axis. At the periphery of the drill it is equivalent to the helix angle
   Point Angle The included angle of the cone formed by the lips
   Lip Clearance Angle The angle formed by the flank and a plane at right angles to the drill axis; the angle is normally measured at the periphery of the drill
   Chisel Edge Angle The obtuse angle included by the chisel edge and a line from either outer corner to the corresponding end of the chisel edge; the angle is measured in a plane perpendicular to the drill axis
 Body:   That portion of the drill extending from the extreme cutting end to the commencement of the shank
 Body Clearance:   That portion of the body surface reduced in diameter to provide diametral clearance
 Chisel Edge:   The edge formed by the intersection of the flanks
 Chisel Edge Corner:   The corner formed by the intersection of a lipand the chisel edge
 Chisel Edge Angle:   The obtuse angle included by the chisel edge and a line from either outer corner to the corresponding end of the chisel edge; the angle is measured in a plane perpendicular to the drill axis
 Diameter:   The measurement across the cylindrical lands at the outer corners of the drill
 Face:   That portion of the flute surface adjacent to the lip on which the chip impinges as it is cut from the work
 Flank:   That surface on the drill point which extends behind the lip to the following flute
 Flutes:   The grooves in the body of the drill which provides lips and permit the removal of chips and allow cutting fluid to reach the lips
 Flute Length:   The axial length from the extreme end of the point to the termination of the flutes at the shank end of the body
 Lands:   The cylindrically-ground surfaces on the leading edges of the drill flutes. The width of the land is measured at right angles to the flute helix
 Lead of Helix: The distance measured parallel to the drill axis between corresponding points on the leading edge of a flute in one complete trun of the flute
 Lip: The cutting edge. The edge formed by the intersection of the flank and face
 Lip Length:   The minimum distance between the outer corner and chisel edge corner of the lip
 Overall Lengths:   The length over the extreme ends of the point and the shank
 Point:   The sharpened end of the drill, consisting of all that part of the drill which is shaped to produce lips, faces, flanks and chisel edge
 Point Angle:  The included angle of the cone formed by the lips
 Rake Angle:   The angle between the face and a line parallel to the drill axis. At the periphery of the drill it is equivalent to the helix angle
 Rotation of cutting:   Right-hand cutting drill  rotates in a counter-clockwise direction when viewed on the point end of the drill. Left-hand cutting drill rotates in a clockwise direction when viewed on the point end of the drill.
 Shank:   That portion of the drill by which it is held and driven
 Web (Core) Taper: The increase in the web or core thickness from the point of the drill to the shank end of the flutes
 Web (Core) Thickness:   The minimum dimension of the web or core measured at the point end of the drill

The Tap and Die Co, London website has a lot of other very useful 'Technical’ Data & Information for you to view