Copper nails, Gripfast nails and metal sheet are dimensioned by wire gauge, where the bigger the number the thinner the nail or sheet.   

Wire Gauges

16g 1.626mm 10g 3.251mm
14g 2.032mm 9g 3.658mm
13g 2.337mm  8g 4.064mm
12g 2.642mm 6g 4.877mm
11g 2.946mm 4g  5.893mm

Pilot Holes for nails

Gripfast Nails

Boat nails

Gauge

Hardwood

Softwood

14

1/16

1/16

3/64

13

-

5/64

1/16

12

1/16

5/64

1/16

11

-

3/32

5/64

10

5/64

3/32

5/64

9

-

3/32

5/64

8

3/32

7/64

3/32

6

-

1/8

7/64