Woodscrews are sized by screw gauge - listed below - where the bigger the number, the bigger the screw

Wood Screw Data

Nominal Diameter

Clearance Hole

Pilot Hole

Gauge

Decimal inch

mm

Hardwood

Softwood

Metal

2

.082

2.08

3/32”

1/16”

-

-

3

.094

2.39

3/32”

1/16”

-

-

4

.108

2.74

7/64”

1/16”

-

5/64”

5

.122

3.10

1/8”

5/64”

-

-

6

.136

3.45

9/64”

3/32”

1/16”

3/32”

7

.150

3.81

5/32”

3/32”

1/16”

-

8

.164

4.17

11/64”

3/32”

5/64”

7/64”or 1/8”

9

.178

4.52

3/16”

7/64”

5/64”

-

10

.192

4.88

13/64”

7/64”

5/64”

9/64”or5/32”

12

.220

5.59

15/64”

1/8”

3/32”

11/64”or3/16”

14

.248

6.30

1/4”

9/64”

7/64”

13/64”or7/32”

16

.276

7.01

9/32”

5/32”

1/8”

-

18

.304

7.72

5/16”

11/64”

1/8”

-

20

.332

8.43

11/32”

3/16”

9/64”

-