API documents published without a type designation, identified by number only.
API identifiers follow: API [Type] [Number]. Types include Std (Standard), RP (Recommended Practice), Spec (Specification), TR (Technical Report), Bull (Bulletin), Publ (Publication), MPMS (Manual of Petroleum Measurement Standards).
API Typeless Standard identifiers are composed of these elements:
API
APIStd, RP, Spec, TR, Bull, Publ, MPMS, COS
RPThe document number
500