physiologically harmless so they are commonly used by the food and drug industries. Standard silicones are resistant to water up to , aliphatic engine and transmission oils and animal and plant oils and fats. Silicones are generally not resistant to fuels, aromatic mineral oils, steam (short term to is possible), silicone oils and greases, acids or alkalis. Fluorosilicone elastomers are far more resistant to oils and fuels. The temperature range of applications is somewhat more restricted. Styrene-butadiene rubber (SBR) Thermoplastics: Thermoplastic elastomer (TPE) styrenics Thermoplastic polyolefin (TPO) LDPE, HDPE, LLDPE, ULDPE Thermoplastic polyurethane (TPU) polyether, polyester: Polyurethanes differ from classic elastomers in that they have much better mechanical properties. In particular they have a high resistance to abrasion, wear and extrusion, a high tensile strength and excellent tear resistance. Polyurethanes are generally resistant to aging and ozone, mineral oils and greases, silicone oils and greases, nonflammable hydraulic fluids HFA & HFB, water up to and aliphatic hydrocarbons. Thermoplastic etheresterelastomers (TEEEs) copolyesters Thermoplastic polyamide (PEBA) Polyamides Melt Processible Rubber (MPR) Thermoplastic Vulcanizate (TPV) Chemical Compatibility: Air, – Silicone Beer - EPDM Chlorine Water – Viton (FKM) Gasoline – Buna-N or Viton (FKM) Hydraulic Oil (Petroleum Base, Industrial) – Buna-N Hydraulic Oils (Synthetic Base) – Viton Water – EPDM Motor Oils – Buna-N Other seals Although the O-ring was originally so named because of its circular cross section, there are now variations in cross-section design. The shape can have different profiles, such as an x-shaped profile, commonly called the X-ring, Q-ring, or by the trademarked name Quad Ring. When squeezed upon installation, they seal with 4 contact surfaces—2 small contact surfaces on the top and bottom. This contrasts with the standard O-ring's comparatively larger single contact surfaces top and bottom. X-rings are most commonly used in reciprocating applications, where they provide reduced running and breakout friction and reduced risk of spiraling when compared to O-rings. There are also rings with a square profile, commonly called square-cuts, lathe cuts, tabular cut or Square rings. When O-rings were selling at a premium because of the novelty, lack of efficient manufacturing processes and high labor content, Square rings were introduced as an economical substitution for O-rings. The square ring is typically manufactured by molding an elastomer sleeve which is then lathe-cut. This style of seal is sometimes less expensive to manufacture with certain materials and molding technologies (compression molding, transfer molding, injection molding), especially in