A nut is an attachment that fits the end of a bolt and strengthens its holding power. The bolt, which is non-tapered, then holds the part fastened with the nut. Both are usually used when both sides of the fastened part need to be accessible. 

If the parts are subject to vibration, an additional component like a spring washer or a lock nut will be necessary to prevent the nut from coming loose.

Bolts and nuts are used to permanently or semi-permanently fasten materials, usually metal. 

Nuts and bolts are used to fasten different materials, such as:

• Metal
• Wood 
• Concrete

Bolts and nuts come in many sizes and types.