Technical Sections

Taps --
Technical information on tapping
Drills --
Technical information on drilling
End Mills --
Technical information on milling
Surface Treatments --
Surface treatment infomation
MSDS --
Material Safety Data Sheet
Thread Mills --
Technical information on Thread Mills

 

To minimize tapping problems and lengthen tool life, use the largest drill possible to produce a minor diameter that will result in the lowest percentage of full thread consistent with adequate strength. A minor diameter that provides a 55% to 65% thread is sufficient for most requirements, but in some cases a higher percentage of thread may be necessary to conform with the minor diameter limits of the thread class specified. Drills generally cut holes larger than their diameters. In the form bellow, the probable percentages of full thread were determined by the average amount oversize the various drills are expected to cut. Reaming becomes necessary when close control of the hole size is required.

Calculate Hole Size for Inch Cutting Taps Calculate Hole Size for Metric Cutting Taps Calculate Hole Size for Inch Forming Taps Calculate Hole Size for Metric Forming Taps

*Generally, deeper than 1 1/2 times the hole diameter.

Suggested Percentage of Full Thread in Tapped Holes
Material		*Deep Hole Tapping	Average Commercial Work	Thin Sheet Stock or Stamping
Free Cutting	Aluminum Brass Bronze Cast Iron Copper Mild Steel Tool Steel	60%-70%	65%-70%	75%-85%
Hard or Tough	Cast Steel Drop Forging Monel Metal Nickel Steel Stainless Steel	55%-65%	60%-70%

1. Hole Size for Inch Cutting Taps
Major Diameter	TPI (threads/inch)	% of Thread
HOLE SIZE

2. Hole Size for Metric Cutting Taps
Major Diameter	Pitch	% of Thread
HOLE SIZE

3. Hole Size for Inch Forming Taps
Major Diameter	TPI (threads/inch)	% of Thread
HOLE SIZE

4. Hole Size for Metric Forming Taps
Major Diameter	Pitch	% of Thread
HOLE SIZE

Suggested Pipe Tap Drill sizes

Tap sizes

1/16

1/8

1/4

3/8

1/2

3/4

1

1-1/4

1-1/2

2

2-1/2

3

3-1/2

4

Drill sizes

Taper Pipe Tap*

D

R

7/ 16

37/ 64

45/ 64

59/ 64

1-5 /32

1-1/2

1-47/64

2-7/32

2-5/8

3-1/4

3-3/4

4-1/4

Straight Pipe Tap**

1/ 14

11/ 32

7/ 16

37/ 64

23/ 32

59/ 64

1-5 /32

1-1/2

1-3/4

2-7/32

2-21/32

*Sizes given permit direct tapping without reaming the hole, but only give a full thread for the first two or three threads. **For Dryseal Straight Pipe Threads suggested drill sizes are as shown, expect; 1/4" pipe, use .444 drill size.