Machinery's Handbook, 31st Edition
956 Twist Drills Shank: That portion of the drill by which it is held and driven. Flutes: The grooves in the body of the drill that provide lips, permit the removal of chips and allow cutting fluid to reach the lips. Web (Core): The central portion of the drill situated between the roots of the flutes and extending from the point end toward the shank; the point end of the web or core forms the chisel edge. Lands: The cylindrical-ground surfaces on the leading edges of the drill flutes. The width of the land is measured at right angles to the flute helix. Body Clearance: The portion of the body surface that is reduced in diameter to provide diametral clearance. Heel: The edge formed by the intersection of the flute surface and the body clearance. Point: The sharpened end of the drill, consisting of all that part of the drill that is shaped to produce lips, faces, flanks, and chisel edge. Face: That portion of the flute surface adjacent to the lip on which the chip impinges as it is cut from the work. Flank: The surface on a drill point that extends behind the lip to the following flute. Lip (Cutting Edge): The edge formed by the intersection of the flank and face. Relative Lip Height: The relative position of the lips measured at the outer corners in a direction parallel to the drill axis. Outer Corner: The corner formed by the intersection of the lip and the leading edge of the land. Chisel Edge: The edge formed by the intersection of the flanks. Chisel Edge Corner: The corner formed by the intersection of a lip and the chisel edge. Table 11. British Standard Drills — Metric Sizes Superseding Gauge and Letter Sizes BS 328: Part 1:1959, Appendix B Obsolete
Recom mended Metric Size (mm)
Recom mended Metric Size (mm)
Recom mended Metric Size (mm)
Recom mended Metric Size (mm)
Recom mended Metric Size (mm)
Obsolete Drill Size
Obsolete Drill Size
Obsolete Drill Size
Obsolete Drill Size
Drill Size
80 79 78 77 76 75 74 73 72 71 70 69 68 67 66 65 64 63 62 61 60 59
0.35 0.38 0.40 0.45 0.50 0.52 0.58 0.60 0.65 0.65 0.70 0.75 0.85 0.90 0.92 0.95 0.98 1.00 1.00 1.05
58 57 56 55 54 53 52 51 50 49 48 47 46 45 44 43 42 41 40 39 38 37
1.05 1.10
36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15
2.70 2.80 2.80 2.85 2.95 3.00 3.30 3.50
14 13 12 11 10
4.60 4.70 4.80 4.90 4.90 5.00 5.10 5.10 5.20 5.20 5.30 5.40 5.60 5.80 6.00 6.10 6.20 1 ⁄ 4 in. 6.50 6.60
I J
6.90 7.00
K L N O P Q R S T U V
3 ⁄ 64 in. 1.30 1.40 1.50
9 ⁄ 32 in. 7.40
M 7.50
9 8 7 6 5 4 3 2 1
7.70 8.00 8.20 8.40 8.60 8.80 9.10 9.30
1.60 1.70 1.80 1.85 1.95 2.00 2.05 2.10 2.20 2.25
9 ⁄ 64 in. 3.70 3.70 3.80
3.90 3.90 4.00 4.00 4.10 4.20 4.30 4.40 4.50 4.60
1 ⁄ 32 in. 0.82
3 ⁄ 8 in. 9.80 10.10 10.30 10.50
A B C D E F G H
W X Y Z
15 ⁄ 64 in.
3 ⁄ 32 in. 2.45 2.50 2.55 2.60 2.65
… … … … … …
17 ⁄ 64 in. … … Gauge and letter-size drills are now obsolete in the United Kingdom and should not be used in the production of new designs. The table is given to assist users in changing over to the recommended standard sizes.
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