2b thread class, right-hand thread direction, hexagon nut style, 0.320 inches minimum and 0.337 inches maximum nut height, w/s:support equipment, b-1 aircraft; shipboard material handling equipment (mhe); sas (starting air sys), ffg-7; fire pumps; vehicle, aircraft refueler r-14; chilled water a/c systems; airborne mobile dir air spt ctl (2id), (o2m jul83)(an/uyq-3a); gun, 5-in./54 cal, mk-42 & 45; l.p. compressors end item identification, 0.5510 inches minimum and 0.5625 inches maximum width across flats

A nut, flat on top and bottom having 6 flat sides. For items which have internal tapered or straight (parallel) pipe threads, specific electrical conduit size designation, and which when installed, provide a method of tightening to lock the connection, see locknut, electrical conduit. See also locknut, tube fitting. For items having a thickness (or height) exceeding two times the width across the flats, use post, electrical-mechanical equipment. (when height or thickness and/or width across the flats is designated as a tolerance dimension, the maximum dimension will be used to determine compliance.)