Nuts, Bolts and Washers
From DT Online
Nuts and Bolts are avilable in a wide variety of sizes, types of screw thread, shapes of head and materials to provide a very commonly used means of fastening components together such that they can be removed if needed.
Machine Screws are very similar to Bolts except that, in general, Bolts have a plain section of shank below the head whereas Machine Screws are threaded right up to the head.
Sizes are now standardised in terms of their diameter in millimetres (e.g. a 10mm bolt has an external diameter of 10mm) although British Association (B.A.) threads may still occasionally be found in the smaller sizes of screws.