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Pilot Holes For Modern Wood Screws In Inches & Millimeters
Choosing The Correct Drill Bit

Many home projects require the use of wood screws, and when using modern wood screws it is advantageous to drill a pilot hole. A pilot hole will keep the screw straight and will aid in preventing the wood from splitting, especially if you are using hardwoods such as oak and maple.

The difference between "traditional wood screws" and "modern wood screws".

Pilot holes for tranditional wood screws.

modern wood screw

Figure 1 - Modern wood screw

With a modern wood screw the pilot hole for the shank and the thread are the same size.

The proper insertion of a wood screw has the shank in the piece of material being held and the thread in the piece of material doing the holding.

joining material with wood screws 1

Figure 2 - Wood screw installed flush with top of lumber.

joining material with wood screws 2

Figure 3 - Wood screw installed below top of lumber to allow for insertion of a wood plug.

Figures 2 and 3 show the relationship of the parts of the wood screw to the material being fastened together

Table 1 defines the correct drill, and countersink size, for modern wood screws in inches:

Table 2 defines the correct drill, and countersink size, for modern wood screws in millimeters:

Table 1 - Drill Size & Countersink Size For Modern Wood Screws - Inches
Screw Size #

4

6

8

9

10

12

14

Pilot Hole For Thread

Hardwood

5/64

3/32

1/8

9/64

5/32

11/64

Softwood

1/16

5/64

7/64

1/8

9/64

5/32

Countersink

C3

C6

C8

C9

C10

C12

C14

 

Table 2 - Drill Size & Countersink Size For Modern Wood Screws - Millimeters
Screw Size #

4

6

8

9

10

12

14

Pilot Hole For Thread

Hardwood

1.5

2

3

3.5

4

5

Softwood

1

1.5

2.5

3

3.5

4

Countersink

C4

C6

C8

C9

C10

C12

C14

Pilot Holes For Lag Bolts