Standard Wood Screw Sizes and Predrilling Recommendations

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

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

By W.L. Fuller