Fasteners and fixings.

Screws, buttons,locks, bolts, pins, brackets, washers, straps, nails and snaps are all fasteners of one type or another.

Applications are often used to name fasteners, industrial fasteners, aerospace fasteners, marine fasteners and building fasteners. Equally so, the materials they are manufactured from, as in stainless steel fasteners, bronze fasteners.

Unlike aluminum, stainless fasteners will not corrode or become brittle as titanium fasteners can. The material can be finished to a degree to suit you. If a bright polished surface of a stainless fastener becomes scratched or suffers minor impact damage it can be refinished. In terms of price most stainless steel fasteners cost far less than aluminium and a fraction of the cost of titanium. Generally, stainless is available in a greater range of sizes.

Threaded fasteners

Of course, not all fasteners are threaded, but many are. Threaded fasteners have differences in what is called their thread form, which is how many 'teeth' that they have for a given length of the threaded shaft.
Different types of threads also have different thread angles (the angle between the 'valleys' of the threads).
There is still a market for imperial fasteners but metric type threads dominate.
Fastener Head Alignment.
Threaded fasteners with different shaped heads will align themselves differently to the surface they are screwed into. This has to be remembered when buying **fasteners, as the length is based upon this alignment. Whether countersunk screws or hexagonal headed screws, they cannot be directly compared by measuring their lengths.
 
Bolt or Set Screw?

the set screw is threaded all the way to the head, the bolt isn't.

Screws

A screw is a mechanism that produces linear motion as it is rotated. The components of a screw are Head, Thread, Shaft, Tip.
Functions of screws are to fix together 2 or more objects, or to compress objects together.

The strength of screw fixation depends on the strength of the screw material, the strength of object material, and the design of screw thread.

The head of a screw stops the screw sinking into the object material being fastened, it provides connection with a screwdriver (allowing the transfer of torque).

Screw come in many shapes - Star screws, hexagonal screws, phillips screws. Undersurface screws are normally rounded to provide maximum surface on undersurface after counter sinking and reducing the zone of excessive stress which may crack the object material being fastened.

Locking screws have thread on the head to allow for locking into plates which provides angular stability.

The strength of a screw is determined by the smallest diameter. The Thread can have various shapes, depth or pitch. Asymetrical threads, ie. flat on the upper surface and rounded underneath, provide a wide surface for pulling and little frictional resistance on the underside. This increases the transfer of torque, pulling 2 objects together as opposed to simply overcoming friction during insertion. Thread depth is half the difference between thread diameter and core diameter. The amount of thread in contact with the material being fastened determines how well the screw resists pull out.
Thread pitch is the linear distance travelled by a screw for a complete (360º) turn of the screw.

Tapping is the process of cutting a thread, some screws are self tapping. Some screws may be self drilling self tapping
Pre tapping allows more of the torque applied to be converted into compressing objects together. Self tapping screws have flutes cut out of the screw tip to allow for cuttings to escape.

Cannulated screws have a hollow core to allow placement over a guide wire.
The lag screw principle allows the compression of two objects, with the screw thread only engaging the object furthest from the head, but allowing compression of the two objects.

Washers

Almost unbelievably, except that we seee them almost everyday, there are many types of washer.

USS, the most common type of washer, is used under the head of a bolt or nut. It has a larger outside diameter to help distribute the forces applied when tightening.
SAE: You see this type in the automotive industry quite often. It is very similar to the USS except that it has a tighter fit to the bolt and has a smaller outside diameter. Fender washers have an over-sized outside diameter but are thinner and usually made with a cheaper material (as opposed to USS). Lock washers are used to help keep the nut from loosening from the bolt. When tightened, the lock washer "locks" the nut in place. External lock washers have external teeth that help lock the nut in place. Internal lock washers have internal teeth that help lock the nut in place. Finishing washers are designed for a flush finish type screw (ie: Flat or oval head screw). The finishing washer has a distinctive cup shape.