This Technical Specification specifies requirements for couplings of 2 in (50,8 mm), 2½ in (63,5 mm), 3 in (76,2 mm) and 4 in (101,6 mm) nominal sizes with ribbed tails and hexagons for use at pressures not exceeding 1 550 kN/m2 (225 lbf/in2). For assembly of coupling, see Figure 1. This document is applicable to couplings which have been designed primarily for aircraft refuelling purposes, but they may also be used for other general purposes.