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Drill Charts
Steel Types

Standard Wood Screw Sizes and Predrilling RecommendationsWood Screw

Screw Size (Gauge)

#2

#3

#4

#5

#6

#7

#8

#9

#10

#12

#14

#16

#18

Head Bore Size

Actual Head Size

11/64

13/64

15/64

1/4

9/32

5/16

11/32

23/64

25/64

7/16

1/2

35/64

39/64

Min. Counterbore Dia.

1/4

1/4

1/4

1/4

5/16

5/16

3/8

3/8

7/16

7/16

1/2

9/16

5/8

Recommended Size

1/4

5/16

5/16

3/8

3/8

3/8

3/8

3/8

1/2

1/2

1/2

5/8

5/8

Screw Shank - Hole Size

3/32

7/64

7/64

1/8

9/64

5/32

11/64

3/16

13/64

7/32

1/4

9/32

5/16

Straight Pilot Drill Size

Hardwood

1/16

5/64

5/64

3/32

7/64

7/64

1/8

9/64

9/64

5/32

11/64

3/16

7/32

Softwood

1/16

1/16

1/16

5/64

3/32

3/32

7/64

1/8

1/8

9/64

5/32

11/64

13/64

Tapered Pilot Drill Size

Hardwood

3/32

7/64

7/64

1/8

9/64

5/32

11/64

3/16

13/64

7/32

1/4

9/32

5/16

Softwood

5/64

3/32

3/32

7/64

1/8

9/64

5/32

11/64

3/16

13/64

15/64

17/64

19/64

Recommended Countersink Number

C3

C4

C4

C5

C6

C7

C8

C9

C102

C12

C14

C169

C18

                                                                                          C14 mounted on TPD

Drill Length Recommendations for Countersink/Taper Point Drill Combos

Screw Size (Gauge)

#2

#3

#4

#5

#6

#7

#8

#9

#10

#12

#14

#16

#18

Tapered Drill Size

3/32

7/64

7/64

1/8

9/64

5/32

11/64

3/16

13/64

7/32

1/4

9/32

5/16

Short Length Drill

Min. Screw Length

1/4

5/16

5/16

3/8

7/16

1/2

5/8

11/16

3/4

7/8

3/4

13/16

7/8

Max. Screw Length *

5/8

11/16

11/16

5/8

11/16

13/16

7/8

15/16

1

1-1/8

1-1/4

1-7/16

1-9/16

Regular Length Drill

Min. Screw Length

3/8

7/16

7/16

1/2

9/16

5/8

3/4

13/16

15/16

1

1-1/8

1-1/4

1-3/8

Max. Screw Length **

 1

1-1/2

1-3/8

1-3/8

1-1/2

1-3/4

1-7/8

2-1/8

2-1/4

2-3/8

2-5/8

2-5/16

2-11/16

Long Length Drill

Min. Screw Length

9/16

9/16

9/16

5/8

11/16

3/4

7/8

15/16

1-1/16

1-1/8

1-5/16

1-7/16

1-9/16

Max. Screw Length***

1-3/4

2

1-7/8

2-1/8

2-3/8

2-3/8

2-3/4

2-3/4

3

3

3-1/8

3-1/16

3-3/16

8” Long Drills

Min. Screw Length

N/A

N/A

N/A

3/4

13/16

1

1-1/16

1-3/16

1-1/4

1-1/4

1-1/2

1-5/8

1-3/4

Max. Screw Length***

N/A

N/A

N/A

4-3/4

4-3/4

4-3/4

4-3/4

4-3/4

4-3/4

4-3/4

4-3/4

4-11/16

4-11/16

                     * = 1/2” to 3/4” of shank for chucking           ** = 3/4” to 1” of shank for chucking         *** = Set screws positioned at end of twist

Anatomy of  a Wood Screw

How to Use This Chart

This chart lists the actual dimensions of wood screws and the closest fractional size equivalents.  The root diameters are measured at the middle of the threaded portion of the screw.  The root diameter on some wood screws tapers along the length of the threads.  If drilling a straight pilot hole, we recommend the same drill size as the root diameter in hardwoods and 15% smaller in softwoods. Head diameters listed are standard for Flat Head and Oval-head screws.  Round Head screws can be 5% to 10% smaller. 

When selecting the wood screw size and length that best suits your requirements, keep in mind that the threaded portion of a wood screw takes up approximately 2/3 of the total length of the screw leaving 1/3 for the shank and head.
Screw-For-Anatomy-Chart

No. Of Screw

Maximum Head Diameter

Shank Diameter

Root Diameter

Threads Per Inch

No. Of Screw

Basic Dec. Size

Nearest Fractional Equivalent

Average Dec. Size

Nearest Fractional Equivalent

0

.119

.060

1/16

Oversize .002

.040

3/64

Oversize .007

32

0

1

.146

.073

5/64

Oversize .005

.046

3/64

Basic Size

28

1

2

.172

.086

3/32

Oversize .007

.054

1/16

Oversize .008

26

2

3

.199

.099

7/64

Undersize .010

.065

1/16

Undersize .002

24

3

4

.225

.112

7/64

Undersize .003

.075

5/64

Oversize.003

22

4

5

.252

.125

1/8

Basic Size

.085

5/64

Undersize .007

20

5

6

.279

.138

9/64

Oversize .002

.094

3/32

Basic Size

18

6

7

.305

.151

5/32

Oversize .005

.102

7/64

Oversize .007

16

7

8

.332

.164

5/32

Undersize .007

.112

7/64

Undersize .003

15

8

9

.358

.177

11/64

Undersize .005

.122

1/8

Oversize .003

14

9

10

.385

.190

3/16

Undersize .002

.130

1/8

Undersize .005

13

10

11

.411

.203

13/64

Basic Size

.139

9/64

Oversize .001

12

11

12

.438

.216

7/32

Oversize .003

.148

9/64

Undersize .007

11

12

14

.491

.242

1/4

Oversize .008

.165

5/32

Undersize .009

10

14

16

.544

.268

17/64

Undersize .002

.184

3/16

Oversize .003

9

16

18

.597

.294

19/64

Oversize .003

.204

13/64

Undersize .001

8

18

20

.650

.320

5/16

Undersize .007

.223

7/32

Undersize .004

8

20

24

.756

.372

3/8

Oversize .003

.260

1/4

Undersize .010

7

24
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