The European Standard series EN 50216 deals with power transformer and reactor fittings. The series, which has been in revision since 2000 and is constantly being supplemented by new parts, now consists of twelve parts. Part 1 is a reference standard containing the general conditions concerning accessories for oil immersed and dry-type transformers and reactors, whereas the remaining parts of the standard each deal with different accessories. This part of the standard DIN EN 50216-12 is the first published edition and deals with requirements and tests for fans for oil-to-air coolers used for transformers as well as fans used for blowing out radiators. Only fans operating axially are dealt with. The standard specifies the dimensions and requirements for ensuring fan interchangeability and uniform fan assembly. The responsible Committee is Subcommittee UK 321.2 "Transformatoren, Leistungen und Abmessungen" ("Transformers, performances and dimensions") of the DKE (German Commission for Electrical, Electronic and Information Technologies) at DIN and VDE.