A wrench or spanner is a tool used to provide grip and mechanical advantage in applying torque to turn objects—usually rotary fasteners, such as nuts and bolts—or keep them from turning.
A set of metric spanners or wrenches, open at one end and box/ring at the other. These are commonly known as “combination” spanners.
Wheel-lock gun of Sigismund III Vasa: The original spanner had a square hole for turning the shaft (r.) of the wheel, which tensioned the mainspring. See also § External links.
Image: Bremsleitungsschluessel
Image: Craftsman Saltus wrenches
A screw is an externally helical threaded fastener capable of being tightened or released by a twisting force (torque) to the head. The most common uses of screws are to hold objects together and there are many forms for a variety of materials. Screws might be inserted into holes in assembled parts or a screw may form its own thread. The difference between a screw and a bolt is that the latter is designed to be tightened or released by torquing a nut.
An assortment of screws, and a US quarter for size comparison
A Brown & Sharpe single-spindle screw machine
A machine screw
Lag screw, also called a lag bolt