DIY How To

DIY Projects - Types of screws and their uses

Screws are made in different lengths and gauges (thickness), they are also made from different materials, depending on what characteristics are required. Screws are designed around strength, corrosion protection and ease of use.

A screw relies on mechanical fixing between itself and the surrounding material for its holding power, therefore a long screw will have more holding power than a short screw of the same gauge. Likewise a higher gauge screw will have more holding power than a lower gauge screw of the same length.

There are many specialist screws available to suit a whole range of applications, there are masonry screws that don't need wall plugs, screws specially for MDF or drywall and a whole host of other screws for specific uses. Many specialist screws are measured in mm but traditional screws are still sold in inches, below is a chart for common traditional screw sizes.

Traditional Screw Sizes

Length

Shank numbers

1/4"

0

1

2

 

4

 

 

 

 

 

 

 

 

 

 

 

3/8"

 

1

2

3

4

 

6

 

8

 

 

 

 

 

 

 

1/2"

 

 

2

3

4

5

6

7

8

 

 

 

 

 

 

 

5/8"

 

 

 

3

4

5

6

7

8

 

 

 

 

 

 

 

3/4"

 

 

 

3

4

5

6

7

8

9

10

12

 

 

 

 

7/8"

 

 

 

 

4

 

6

7

8

 

 

 

 

 

 

 

1"

 

 

 

3

4

5

6

7

8

9

10

12

14

 

 

 

11/4"

 

 

 

 

4

5

6

7

8

9

10

12

14

 

 

 

11/2"

 

 

 

 

4

 

6

7

8

9

10

12

14

16

 

 

13/4"

 

 

 

 

 

 

6

7

8

9

10

12

14

16

 

 

2"

 

 

 

 

 

 

6

7

8

9

10

12

14

16

18

20

21/4"

 

 

 

 

 

 

6

 

8

 

10

12

14

 

 

 

21/2"

 

 

 

 

 

 

6

 

8

9

10

12

14

16

 

 

23/4"

 

 

 

 

 

 

 

 

8

 

10

12

14

 

 

 

3"

 

 

 

 

 

 

6

 

8

 

10

12

14

16

18

 

31/2"

 

 

 

 

 

 

 

 

8

 

10

12

14

16

 

 

4"

 

 

 

 

 

 

 

 

8

 

10

12

14

16

18

20

 

Screw Head Types and Uses

The length of the screw is measured from different points according to the head type.

Screw types

There are different type screw heads which require different screwdrivers. Slotted head screws require the normal flat blade screwdrivers, whereas crossheads screws are either philips or pozidrive. A philips screw requires a philips screwdriver whereas with a pozidrive screw both philips and pozidrive screwdrivers will fit. Crosshead screws allow more power to be applied to the screw without the screwdriver slipping, thus helping reduce any damage to the head itself and also to the surrounding area. Make sure the correct size screwdriver is used.

Screw head types

 

Countersunk screw
Countersunk screw

Countersunk screws are used where the head must end up being flush with the surface, to make the hole for the countersink head to fit into use a countersink bit, or a special combined drill bit that drills the hole and countersinks at the same time.

Round head screw
Round head screw

Round head screws are used for assemblies that may be dismantled and material that is too thin to be countersunk. Sometimes a washer is used, especially if the material being fastened is very thin.

Some round head screws are designed to be used with dome covers, which produces a nice finish for areas of decoration.

Raised head screw
Raised head screw

Raised head screws are a combination of the above two and are used for areas where a neat finish is needed.

There are screw cups that can be used in conjunction with raised head screws, these provides a greater surface area for the screw to grip and also look neater.

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