Abstract: An automatic coupling for the joining of two pipes has a male element and a female element with an internal bore to receive the male element. The female element incorporates a locking member arranged to engage behind an annular shoulder on the male element, and retain the male element in the female. The locking member is slideable transversely to the bore in the female element, and has a keyhole shaped opening through it. The shoulder passes through the wider part of the keyhole opening after which a return spring engages the narrower part of the keyhole opening behind the shoulder.To provide an automatic coupling action the narrower part of the keyhole opening has two doubly oblique surfaces. When the male element is inserted, a frusto conical leading surface to the shoulder bears on these doubly oblique surfaces and displaces the locking member against the return spring to allow the shoulder to pass through the wider part of the keyhole opening.