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What are coarse-threaded screws
and fine-threaded screws?

 
         
     

Screws are either coarse-threaded or fine-threaded.

 
         
  Coarse threaded black carcass screw  

Coarse-threaded screws have a greater pitch (more space between each thread).

 
         
  Fine-threaded machine screw  

Fine-threaded screws have a smaller pitch (less space between each thread).

 
         
     

Coarse-threaded screws

 
  A fine-threaded screw taking less time to insert  

Compared to fine-threaded screws, coarse-threaded ones takes less time to insert or remove. This is because the screw travels further in one rotation due to the greater space between threads.

 
         
  Crooked screw in piece of wood  

Coarse-threaded screws are less likely to jam if the screw is inserted at an angle.

 
         
  Coarse threaded screws with soft materials  

Coarse-threaded screws are used in softer materials such as soft/hard wood, plastic or plasterboard. This is because their threads are able to grip the soft fibres of the material and hold the screw in place.

 

A fine-threaded screw would be more likely to slip out of soft material.

 
         
  Gold screw with coarse threads and serrated edges  

Coarse threads with serrated edges

The coarse threads on some screws have sharp serrated edges. Manufacturers claim that this allows the threads to cut more easily through the fibres of the material.

 

Screws with serrated threads tend to be more expensive.

 
         
     

Fine-threaded screws

 
  Fine threaded screw taking more time  

Compared to coarse-threaded screws, fine-threaded ones takes more time to insert or remove. This is because the screw does not travel as far in one rotation due to the smaller space between threads.

 

Because a fine-threaded screw takes longer to insert or remove, it allows for finer adjustment when working.

 
         
  Fine threaded screws with hard materials  

Screws with fine threads are used in harder materials such as metal and are usually inserted into a tapped hole.Their fine threads allow them to be secured extremely tightly in hard materials.

 

A coarse-threaded screw would not be able to clamp two hard materials together because of the large gap between each thread.