How to select the correct screwdriver
bit for the screw

The screwdriver bit you need will depend on the size of screw you want to insert or remove.

Step 1 – Identify the screw’s drive design

Examine the screws you want to insert or remove. What type of drive do they have?

The most common drive designs are:

• Slotted

• Phillips

• Pozidriv

• Torx

• Square/Robertson

• No drive, just a hexagonal head
   

If you’re unsure, see our section: What are the different drive designs?

Step 2 – Find out the screw’s size

Now that you know what type of screwdriver bit to use, you need to select the correct size. This will ensure that the bit doesn’t slip out of the screw head when inserting or removing it.

A screw’s size is presented as a number. This number does not refer to a particular dimension on the screw, it refers to size in the same way as a size 5 shoe or a size 10 dress.

The higher the number, the larger the overall size of the screw.

The screw’s number can be found on the product packaging or you can find it out by measuring the shank of the screw and looking at the table below.

Fully and partially-threaded screws

To find out the number of a fully-threaded screws (right) the measurement is taken across the body of the screw.

For partially-threaded screws (left) it is taken across the smooth portion of the shank. Once you have this measurement, look at the table below.

Step 3 – Look at the table below

Look along the table to find out the screw’s number and the size of screwdriver bit needed to insert or remove it.

For example,  if you had a pozidriv screw with a shank diameter of 3.0 mm, you can see from the table that it’s a number 4 screw and needs a PZ1 screwdriver bit to insert or remove it.

Please note – this table does not apply to machine screws. Only screws with a tapered body ending in a point.

Screw gauge / shank diameter (mm)

Square / Robertson screwdriver bit

Blade length

(mm)

Blade width

(mm)