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Screw Dimensions


Wood Screw Dimensions

 

Boring Chart for Wood Screws

How to use this chart:

The table of wood screw specifications simplifies the selection of the bit or drill size best suited to your rquirements. The fractional equivalents and undersize or oversize decimals indicate how close a bit of given fractional size will bore to the actual screw dimension and whether the fit will be snug or loose. In selecting a tool size for the pilot hole (for the threaded portion of the screw), note that root diameters are average dimensions measured at the middle of the threaded portion. On some screws the root diameter tapers slightly from the end to the smooth shank. It is usually good practice to bore the pilot hole the same size as the root diameter in hardwoods, and about 15% smaller in softwoods.

The SHANK DIAMETERS shown below are standard specifications subject to tolerances of plus 0.004" and minus 0.007".

MAXIMUM HEAD DIAMETERS are also standard specifications which apply to flathead and ovalhead screws. Head sizes run 5% to 10% smaller in roundhead screws.

Number of THREADS PER INCH is rounded to the nearest whole number; this is especially noticeable in the larger sizes.

Wood Screw to standard specifications

#

 

Shank Diameter

Root Diameter

 

 #

 of Screw

 Max. Head Dia.

Basic Dec. Size

Nearest Fractional Equivalent

Avg. Dec. Size

Nearest Fractional Equivalent

Threads Per Inch

of Screw

0

.119

.060

1/16

Oversize .002

.040

3/64

Oversize .007

32

0

1

.146

.073

5/64

Oversize .005

.048

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

Oversize .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

12

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

22

.680

.348

11/32

Undersize .004

 .241

15/64

Undersize .007

7

22

24

.756

.372

3/8

Oversize .003

.260

1/4

Undersize .004

7

24

28

.835

.422

27/64

Undersize .001

.280

9/32

Oversize .001

6

28


Countersink Chart

 

 

Use Type "C" (Carbon Steel) Countersinks, with your taper-point, brad-point, or regular-point drill bits, to drill countersunk pilot holes for your wood screws.

Type C Countersink

Type "C" Countersinks, for pre-drilling in wood

Stock Number

Cutting Diameter

Pilot Drill Size

Overall Length

 

Stock Number

Cutting Diameter

Pilot Drill Size

Overall Length

                 
         

C122

1/2

1/8

7/8

         

C129

1/2

9/64

7/8

C2

1/4

5/64

3/4

 

C125

1/2

5/32

7/8

C3

1/4

3/32

3/4

 

C1211

1/2

11/64

7/8

         

C92

1/2

3/16

7/8

         

C102

1/2

13/64

7/8

C4

5/16

7/64

7/8

 

C12

1/2

7/32

7/8

C44

5/16

1/8

7/8

 

C1415

1/2

15/64

7/8

C65

5/16

9/64

7/8

 

C14

1/2

1/4

7/8

C410

5/16

5/32

7/8

 

 

     

C411

5/16

11/64

7/8

 

C145

5/8

5/32

1-1/16

C43

5/16

3/16

7/8

 

C143

5/8

3/16

1-1/16

         

C167

5/8

7/32

1-1/16

         

C16

5/8

1/4

1-1/16

C56

3/8

3/32

7/8

 

C1617

5/8

17/64

1-1/16

C57

3/8

7/64

7/8

 

C169

5/8

9/32

1-1/16

C5

3/8

1/8

7/8

 

C1619

5/8

19/64

1-1/16

C6

3/8

9/64

7/8

 

C18

5/8

5/16

1-1/16

C7

3/8

5/31

7/8

         

C8

3/8

11/64

7/8

 

C243

3/4

3/16

1-1/8

C9

3/8

3/16

7/8

 

C247

3/4

7/32

1-1/8

C913

3/8

13/64

7/8

 

C244

3/4

1/4

1-1/8

C97

3/8

7/32

7/8

 

C245

3/4

5/16

1-1/8

         

C20

3/4

21/64

1-1/8

         

C24

3/4

3/8

1-1/8

C105

7/16

5/32

7/8

       

 

C1011

7/16

11/64

7/8

 

C284

7/8

 1/4

1-1/4

C103

7/16

3/16

7/8

 

C285

7/8

5/16

1-1/4

C10

7/16

13/64

7/8

 

C286

7/8

3/8

1-1/4

C1014

7/16

7/32

7/8

 

C287

7/8

7/16

1-3/8

C104

7/16

1/4

7/8

         
         

C324

1"

1/4

1-3/8

 

       

C326

1"

3/8

1-3/8

         

C328

1"

 1/2

1-1/2