This part of EN 1555 specifies the characteristics of fusion fittings made from polyethylene (PE) as well as of mechanical fittings for piping systems in the field of the supply of gaseous fuels. It also specifies the test parameters for the test methods referred to in this standard. In conjunction with Parts 1,2,4 and 5 of EN 1555, it is applicable to PE fittings, their joints and to joints with components of PE and other materials intended to be used under the following conditions: a) a maximum operating pressure, MOP, up to and including 10 bar ); b) an operating temperature of 20 °C as reference temperature. NOTE 1 For other operating temperatures, derating coefficients should be used; see EN 1555 5. EN 1555 (all parts) covers a range of maximum operating pressures and gives requirements concerning colours and additives. NOTE 2 It is the responsibility of the purchaser or specifier to make the appropriate selections from these aspects, taking into account their particular requirements and any relevant national regulations and installation practices or codes. This standard is applicable for fittings of the following types: a) electrofusion socket fittings; b) electrofusion saddle fittings; c) spigot end fittings (for butt fusion using heated tools and electrofusion socket fusion); d) mechanical fittings. The fittings can e.g. be in the form of couplers, equal and reduced tees, reducers, bends or caps.