DRILLS AND TAPS





Tapping threads is a fairly simple procedure so long as a few simple rules are followed.

To avoid breaking a tap , (which is a hassle to extract ) always remember the fore mentioned rules. The following charts show which drill sizes are required for a standard 75% depth cut thread . These should be followed as closely as possible , although in a pinch I have gotten lucky and used the next closest drill bit, but this practice is not recommended. Lubricants are of the utmost importance and should always be used when applicable , the following suggested lubricants should be used whenever possible but quite often I will use ordinary engine oil with satisfactory results. There are 4 basic types of taps they are plug tap which is typically used for pipe threads, taper tap which are used for tapping a work piece in which the hole goes clean through the metal, bottoming taps are used when the hole stops part way through the work piece, and finally spiral fluted taps, these are premium taps with helical relief cuts and are well suited for cutting worm gears. When tapping threads always remember back cutting, make a foreward rotation of 1/2 to 3/4 revolution and then reverse 1/4 turn until you feel the cuttings break off then resume foreward tapping.




STANDARD THREADS

Size - Thread Drill Size Size - Thread Drill Size
1/16 - 64 3/64 9/16 - 18 33/64
3/32 - 48 #49 5/8 - 11 17/32
1/8 - 40 #38 5/8 - 18 37/64
5/32 - 32 1/8 11/16 - 11 19/32
5/32 - 36 #30 11/16 - 16 5/8
3/16 - 24 #26 3/4 - 10 21/32
3/16 - 32 5/32 3/4 - 16 11/16
7/32 - 24 #16 7/8 - 9 49/64
7/32 - 32 3/16 7/8 - 14 13/16
1/4 - 20 13/64 1-8 7/8
1/4 - 24 #4 1-12 59/64
1/4 - 28 7/32 1-14 15/16
1/4 - 32 7/32 1 1/8 - 7 63/64
5/16 - 18 F 1 1/8 - 12 1 3/64
5/16 - 24 I 1 1/4 - 7 7/64
5/16 -32 9/32 1 1/4 - 12 1 11/64
3/8 -16 5/16 1 3/8 - 6 1 11/64
3/8 - 24 Q 1 3/8 - 12 1 19/64
7/16 -14 3/8 1 1/2 - 6 1 11/32
7/16 -20 25/64 1 1/2 - 12 1 27/64
1/2 - 12 27/64 1 5/8 - 5 1/2 1 7/16
1/2 - 13 27/64 1 3/4 - 5 1 9/16
1/2 - 20 7/16 1 7/8 - 5 1 11/16
9/16 - 12 31/64 2 - 4 1 13/16



METRIC THREADS

Size - Pitch (mm) Drill Size (mm) Size  - Pitch (mm) Drill Size (mm)
1.5 - 0.35 1.1 12 - 1.25 11
2 - 0.40 1.6 12 - 1.50 10.5
2 - 0.45 1.5 12 - 1.75 10.5
2 - 0.50 1.5 13 - 1.50 11.5
2.3 - 0.40 1.9 13 - 1.75 11.5
2.5 - 0.45 2 13 - 2.00 11
2.6 - 0.45 2.1 14 - 1.25 13
3 - 0.50 2.5 14 - 1.75 12.5
3 - 0.60 2.4 14 - 2.00 12
3 - 0.75 2.25 15 - 1.75 13.5
3.5 - 0.60 2.9 15 - 2.00 13
4 - 0.70 3.3 16 - 2.00 14
4 - 0.75 3.25 17 - 2.00 15
4.5 - 0.75 3.25 18 - 1.50 16.5
5 - 0.75 4.25 18 - 2.00 16
5 - 0.80 4.2 18 - 2.50 15.5
5 - 0.90 4.1 19 -2.50 16.5
5 - 1.00 4 20 - 2.00 18
5.5 - 0.75 4.25 20 - 2.50 17.5
5.5 - 0.90 4.6 22 - 2.50 19.5
6 - 1.00 5 24 - 3.00 21
6 - 1.25 4.8 26 - 3.00 23
7 - 1.00 6 27 - 3.00 24
7 - 1.25 5.8 28 - 3.00 25
8 - 1.00 7 30 - 3.50 26.5
8 - 1.25 6.8 32 - 3.50 28.5
9 - 1.00 8 33 - 3.50 29.5
9 - 1.25 7.8 34 - 3.50 30.5
10 - 1.25 8.8 36 - 4.00 32
10 - 1.50 8.6 38 - 4.00 34
11 - 1.50 9.6 40 - 4.00 36



PIPE THREADS

Size - Thread Tap Drill Size
NPT (taper) NPS (straight)
Inches MM Inches MM
1/8 - 27 Q 8.5 11/32 8.75
1/4 - 18 7/16 11 7/16 11.5
3/8 - 18 9/16 14.5 31/64 15
1/2 - 14 45/64 18 23/32 18.5
3/4 - 14 29/32 23 50/64 23.5
1 - 11 1/2 1 9/64 29 1 5/32 29.5
1 1/4 - 11 1/2 1 31/64 38 1 1/2 38.5
1 1/2 - 11 1/2 1 47/64 44 1 3/4 44.5
2 - 11 1/2 2 13/64 56 2 7/32 57



MACHINE THREADS

Size - Thread

 Tap Drill Size Size - Thread Tap Drill Size
0 - 8 3/64 6 - 32 #36
1 - 56 #54 6 - 36 #34
1 - 64 #53 6 - 40 #33
1 - 72 #53 8 - 32 #29
2 - 56 #50 8 - 36 #29
2 - 64 #50 8 - 40 #28
3 - 48 #47 10 - 24 #25
3 - 56 #45 10 - 30 #22
4 - 32 #45 10 - 32 #21
4 - 36 #44 12 - 24 #16
4 - 40 #43 12 - 28 #14
4 - 48 #42 12 - 32 #13
5 - 40 #38 14 - 20 #10
5 - 44 #37 14 - 24 #7



TAPPING LUBRICANTS CHART




Material Being Cut Lubricant
  • Types of Steel
  • Cast
  • Forged
  • Machined
  • Stainless
  • Tool
  • Chromium
  • Chromemoly
  • nickel
  • vanad
  • manganese
  • malleable irons
  • Sulfur Base Oil
  • Cast Iron
  • Synthetic Resins
  • Hard Fuller
  • Dry - No Lubricant
  • Brass
  • Bronze
  • Copper
  • Manganese bronze
  • Light Oil
  • Aluminum
  • Duralumin
  • Die Castings
  • Kerosene
  • WD-40



INDEX