It's all about the icons

Mission: Travel to Finland and find Solarflare.

Original mission: See the arctic circle and be photographed in different environments.

A screw is a shaft with a helical groove or thread formed on its surface. Its main uses are as a threaded fastener used to hold objects together, and as a simple machine used to translate torque into linear force. It can also be defined as an inclined plane wrapped around a shaft.

Threaded fastener

A screw used as a threaded fastener consists of a shaft, which may be cylindrical or conical, and a head. The shaft has a helical ridge or thread formed on it. The thread is essentially an inclined plane wrapped around a shaft. The thread mates with a complementary helix in the material. The material may be manufactured with the mating helix (tapped), or the screw may create it when first driven in (a self-tapping screw). The head is specially shaped to allow a screwdriver or wrench to grip the screw when driving it in. It also stops the screw from passing right through the material being fastened and provides compression.

Screws can normally be removed and reinserted without reducing their effectiveness. They have greater holding power than nails and permit disassembly and reuse.

A screw that is tightened by turning it clockwise is said to have a right-hand thread. Screws with left-hand threads are used in exceptional cases, when the screw is subject to anticlockwise forces that might undo a right-hand thread. Examples include rotating items such as the left hand grinding wheel on a bench grinder or the left hand pedal on a bicycle (both looking towards the equipment).

Threaded fasteners are traditionally made by a cutting action such as taps and dies provide, however recent advances in tooling allows them to be made by rolling the blank (a section of rod) between two specially machined dies. The thread form and shape of the fastener are squeezed onto the blank. (Surprisingly, shot pellets can be made in a similar fashion.) This method work hardens the threads and saves material, but there are those who believe the cut product was superior.

Source: http://en.wikipedia.org/wiki/Screw