Size of Screws and Metric Imperial Screw Conversion Chart

Summary: In this project we deal with the different sizes of screws and the conversion from metric to imperial sizes using our very handy conversion chart. Also find out about the different types of wood screws available.

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Screw sizes are a mystery to most people so we have tried to make life a little easier with the metric imperial screw conversion chart below.

A wood screw is sized by two different numbers. First is the diameter of the screw – the larger the number, the larger the diameter. A number 4 screw is much smaller than a number 12 screw.

The length is given next and it should be remembered that the length given for a screw is the length that is buried in the wood or other material, it does not include the head of a raised, or domed headed screws.

Phillips head screw

Phillips head screw

Slotted screws are fast becoming history and cross head screws are now the fashion but it must be remembered that a cross head screw can either be a Philips screw (above image)or a pozidrive/supadrive screw (below image). They both require a different driver which can be found below.

Pozidrive head screw

Pozidrive head screw

See also our projects on different types of screw and how to countersink.

Metric Imperial Screw Conversion Chart

Gauge (mm) Length (mm) Imperial Size
3mm 12 4 x 1/2
16 4 x 5/8
20 4 x 3/4
25 4 x 1
30 4 x 1 1/4
40 4 x 1 1/2
3.5mm 12 6 x 1/2
16 6 x 5/8
20 6 x 3/4
25 6 x 1
30 6 x 1 1/4
40 6 x 1 1/2
4mm 12 8 x 1/2
16 8 x 5/8
20 8 x 3/4
25 8 x 1
30 8 x 1 1/4
35 8 x 1 3/8
40 8 x 1 1/2
45 8 x 1 3/4
50 8 x 2
60 8 x 2 3/8
70 8 x 2 3/4
4.5mm 25 9 x 1
30 9 x 1 1/4
35 9 x 1 3/8
40 9 x 1 1/2
45 9 x 1 3/4
50 9 x 2
60 9 x 2 3/8
70 9 x 2 3/4
75 9 x 3
5mm 25 10 x 1
30 10 x 1 1/4
35 10 x 1 3/8
40 10 x 1 1/2
45 10 x 1 3/4
50 10 x 2
60 10 x 2 3/8
70 10 x 2 3/4
75 10 x 3
80 10 x 3 1/4
90 10 x 3 1/2
100 10 x 4
6mm 30 12 x 1 1/4
40 12 x 1 1/2
50 12 x 2
60 12 x 2 3/8
70 12 x 2 3/4
75 12 x 3
80 12 x 3 1/4
90 12 x 3 1/2
100 12 x 4
110 12 x 4 3/8
130 12 x 5 1/8
150 12 x 6

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