Should a washer go on nut side, or the bolt side?

Question

Often I take something apart and when I go to reassemble it, I don't remember which side the washer was on. When there's only one washer, does it generally go on the nut side (pressed up against the nut) or the bolt side (pressed up against the bolt)?

Answer 1

If there was only one washer, it generally will go on the nut side as the nut has less surface area in contact with the thing being connected than the bolt side.

Answer 2

Triple use (as I saw after years of mechanics) :

1) Washers are ofter used to avoid grinding of the support when you screw the nut.

2) Washers avoid the bolt head or the nut to penetrate/damage the support.

3) Washers help things moving in boltened assemblies if you oil them a bit (eg. articulations).

Answer 3

If you are fastening pieces of lumber together you will want to put washers on both the nut and bolt head sides. Otherwise as was pointed out it generally goes inside of the nut, outside of and against the fastened piece.

Answer 4

If there is only one washer used with a nut/bolt, it usually goes on the nut side.

The nut in most circumstances is more movable, and is more commonly turned to tighten the assembly. The washer helps prevent damage to the surface of the object being fastened. In most cases where the bolt is easier to turn, the bolt has a round head that will cause less damage anyway.

For the same reason, lock washers always go on the nut side to stop the nut moving. Lock washers are almost always used with a flat washer as well.

The nut is also often smaller in profile than the bolt head. Not always, but often. The washer helps distribute the pressure that the nut places on the surface of the fastened objects.

Answer 5

Washers are used for multiple purposes when mechanical parts are assembled using bolts and nuts. Here are some usages and as you can see it is not likely that a generalized answer can be devised to directly answer your question!

1. Some washers have a special design that attempts to help keep the nut and/or bolt from coming loose. Known as a lock washer these may be a split ring type, star type, wavey or any one of a number of other designs. A lock washer will be used with the part of the assembly that most likely could turn such as the nut. It could be used under the bolt head in instances where the bolt screws into threads in one part of the assembly.

2. A washer is sometimes used to protect the surface of the assembled parts. A nut or bolt head being turned during the tightening process can mar the part surface around the hole and a washer can be used to take the abuse as opposed to the part. This may be particularly applicable when the parts are a softer material such as plastic, brass or aluminum and a washer made of a harder material is used.

3. Sometimes a thin material is part of the assembly and a larger diameter washer is used to help distribute the pressure of the tight bolt across a larger part of the thin material. In these cases the washer would be used against the thin material. It can help to keep the material flatter or to prevent pullout of the fastener.

4. Assemblies often have a slotted or oversize hole on one side. This is designed to allow for tolerance in the hole size and location in the parts being assembled. Another variation of this would be a long slotted hole that permits the adjustment of one part relative to the other before the bolt and nut are fully tightened. A washer would be used over the slotted hole to allow the pressure of the tightened bolt to be spread across the slot and up onto the part itself. In some instances the washer will also help to prevent the turning bolt head or nut from deforming the slotted part during the tightening process.

5. Some assemblies are designed to have the parts move with respect to one another when the bolt is actually tight. The travel of the nut may be restricted by a shouldered design of the bolt or a sleeve can be installed around the bolt in the hole. In these cases a washer is often used to allow the moving part from wearing the bolt head or nut. The washer may be made of a material designed to reduce the friction between itself and the moving part. This can also help to keep a turning part from trying to loosen the nut through friction.

Many times washers will play a role that is a combination of the above usages. One common example is to see a lock washer used along with a larger diameter flat washer.