Why Use Washers in Bolted Joints?

Lock Washers

• Lock washers, which hold the nut firmly on the bolt after tighteningwashers image by Greg Pickens from Fotolia.com
  
  Lock washers are cut and slightly bent. Their main purpose is to "lock" the nut in place by exerting an uneven force on the face of the nut. Lock washers are often used in addition to standard washers.
  
  

Flat Washers

• Hex head bolts with machine washers and locking nutsstainless steel image by Tom Oliveira from Fotolia.com
  
  The main purpose of a flat washer is to provide a larger surface for a bolt to exert pressure. Used on wood or other soft materials, flat washers help to keep bolts from pulling through material.
  
  

Washer Size

• An assortment of nuts, bolts and washersScrews on work table image by millis from Fotolia.com
  
  The correct size washer should be used with a nut and bolt. The washer should carry the same size designation as the bolt, such as 1/4 inch or #10. Using a washer that is too large may cause the bolt or nut to pull through the washer.
  
  

Specialty

• Brass lock washers, which are often used in lamp constructionRondelles image by Tjall from Fotolia.com
  
  Specialty washers are used with different materials for different purposes. They might be spacers or special-purpose locking washers.
  
  

Position

• A hex head bolt with nut, lock washer and washernut and bolt image by sheldon gardner from Fotolia.com
  
  Lock washers are placed closest to the nut, while flat washers are closest to the material being bolted. Adding a second machine washer between the bolt head and the material is a good way to add strength.