Beryllium, in the bicycle industry is beginning to get the glimmer of a magic metal. While it was both unheard of and unused in the bike industry in 1990, parts made of beryllium are now starting to trickle into the industry. Beryllium is a specialty metal that is steel-grey metal in color, with an extremely low density, making it very light weight. At 1.85 grams to the cubic centimeter, its density compares to that of magnesium. It is also a high strength metal, making it possible to design light weight, thin membered parts with a high stiffness. A column made of beryllium to support a load placed directly downward on top of it, will have a greater load carrying capacity, and be lower in weight than any other metal of equal size. Until the 1950's beryllium was used principally as an alloying element in copper and nickel to produce age hardening (defined in the aluminum section) alloys for springs, electrical contacts, spot welding electrodes, and non-sparking tools. Beryllium was also used in the initiating of fission chain reactions in the first atomic bombs. Within the plutonium core of the bomb, which was about the size of an orange, it was used to make the "initiator". Neutrons are needed to start a fission chain reaction and the initiator is what provided them. The initiator was made of polonium, which gives off alpha radiation, and beryllium, which, when hit by alpha radiation, emits neutrons. The two metals were packaged separately in a sphere about the size of a hazelnut that was surrounded by two stage explosives one slow acting and another fast acting and lens focused. When the primary implosion from the explosives in the bomb reached the metals, they would be bought together, and neutrons would be let off, starting the chain reaction. Presently beryllium is added to aluminum and magnesium to produce metallurgic grain refinement and oxidation resistance. Beryllium has a high thermal capacity or "specific heat" (the ratio of the heat capacity of a material to the heat capacity of water), which makes the metal useful for electronic heat sinks, aircraft disc brakes, and rocket heat shields. A pound of beryllium will absorb as much heat as five pounds of copper or two pounds of aluminum. Unalloyed beryllium is produced in two grades, structural (S) and instrument (I). The structural grade has less beryllium oxide because increasing amounts of the oxide limit the metals formability. The structural grade is what is frequently used in the aerospace industry for satellites, aircraft disc brakes and rocket nozzles. The instrument grade is used for gyroscopes, inertial guidance systems, X-ray tube windows, and because its light weight yet very strong, precision satellite and airborne optical components. Stock beryllium mill products are made from beryllium powder that has been consolidated into a block by hot vacuum pressing. The powder is made by chipping and mechanically pulverizing previously vacuum cast ingots (see "Titanium"). The hot vacuum pressed block is then rolled into sheet, bar, rod, or billet mill products. Billets can be extruded into other shapes. Cold working of the beryllium material may exhibit strong anisotropy (term described in the aluminum section). The exact tensile strength of a finished beryllium product will vary therefore, with the metals processing method. Beryllium has three industrial disadvantages in its use. They are its high cost, potential toxic hazards from inhaling during machining, and a tendency for brittleness at room temperature, (remember increased metal strength comes from a tight stable grain, the more compressed the grain the stronger and stiffer the metal, the stronger and stiffer the metal the less ductile it is, lack of ductility is also known as brittleness). Beryllium and beryllium oxide are toxic. Dust, fumes and vapors during the machining or processing of beryllium into finished goods, through inhalation or ingestion, should be avoided. Beryllium finished goods and solid beryllium are considered non-hazardous.