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How to select the correct screwdriver bit for the screw?


How to select the correct screwdriver
bit for the screw

  Screwdriver bits  

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

  Screw with labelled top; The slot on the top of the screw's head is called its drive  

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

  Screw drive designs  

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.

  Cardboard box  

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.

  Shank diameter of partially threaded and fully threaded screw  

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

  Pozidriv screw and screwdriver bit  

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 number

Screw gauge / shank diameter (mm)

 Philips Screwdriver bit  Pozidriv Screwdriver bit  Torx Screwdriver bit

Square / Robertson screwdriver bit

Flat blade screwdriver bit     

Shank diameter 

Philips screw drive Pozidriv screw drive Torx screw drive

Square screw drive 

Blade length


Blade width


   2  2.0  PH1  PZ1  T8  00      
   3  2.5  PH1  PZ1    0      
   4  3.0  PH1  PZ1  T10  0      
   6  3.5  PH2  PZ2  T15  4.5  0.6  
   8  4.0  PH2  PZ2  T20  2  5.5  0.8  
   9  4.5  PH2  PZ2      6.5  1.2  
   10  5.0  PH2  PZ2  T25  2  6.5  1.2  
   11  5.5  PH3  PZ3      6.5  1.2  
   12  6.0  PH3  PZ3  T30  3      
   13  6.5  PH3  PZ3          
   14  7.0  PH3  PZ3    3  8.0  1.6  


Wonkee Donkee says; Now you have the correct screwdriver bit for your screws you can begin work! To ensure your screwdriver bit fits into the chuck of your power tool, see section ‘chuck size’. If you want to extend the reach of your tool or alter its angle, then consider using a bit holder. For more information, see the ‘bit holder’ section.

Wonkee Donkee Tools