The 90 degree elbows are used to connect tubes at a 90° angle. As the name suggests, the elbow is always a right-angle in shape. Such type of elbow is also known as "90 bends or 90 ells". This is a pipe fitting device that is bent in such a way to produce a 90° change in the direction of flow of the fluid/gas in the pipe. The elbow is used to change the direction in piping and is also sometimes called a "quarter bend".
http://www.zhijusteel.com/elbow/90-degree-elbow/

Bismuth-based: Bismuth alloys will have a composition that is less of a ductile characteristic than tin, as it can become brittle. Manufacturers use bismuth due to its expansion qualities when it melts and then solidifies as it can expand to up to 3.3%. The more bismuth is in an alloy, the more it expands. It is less expensive than other alloys that are featured and the least toxic as it can be used in applications where there is drinking water present. ;
http://www.wocmetal.com/low-me....lting-alloys/bismuth

A properly functioning HVAC system is essential to a comfortable home. While many people know how to operate their AC system, very few people know how it actually works. Your AC’s return air vent is a critical component of an HVAC system and serves several purposes. Not only do return air vents maintain your home’s air pressure and filter out debris, but they can also serve to save you on energy costs and expenses.
http://www.sxcanreal.com/return-air-vent/

Preforms are manufactured from polyethylene terephthalate (PET), so they are called PET preforms. They are produced by RETAL using a highly-accurate injection molding process on equipment from the leading world vendors.
Preform weight depends on the end container’s desired volume. Preforms can be single-layer or multilayer. Barrier preforms provide additional benefits and increased beverage shelf life, thanks to a special layer embedded in several layers of polyethylene terephthalate.http://www.sjzwlplastic.com/pet-preform/

Most strings in an acoustic piano are grouped in threes, with each group tuned to the same note. When played normally, the hammer strikes all three at the same time giving a full, bright sound. On a grand piano, the una corda pedal shifts the entire mechanism to the right, so the hammer only hits two of the three strings.
http://www.sihaimetal.com/piano-pedal/