A subsea female coupler has a body defining a socket for the reception of a probe of a male coupler. The socket includes an annular shoulder and, outwardly of the shoulder, a part-conical seat which tapers towards the interior of the socket. An annular seal is disposed to provide radial sealing between the socket and the probe and is positioned in the annular shoulder. A metal retainer in the form of a securing ring, which has a bevelled rim for abutment with the seat, provides sealing between the region of the seal and the exterior of the body of the coupler. The retainer has a screw-threaded periphery for engagement with a complementary thread on the interior of the socket. An inner ring liner fits within the retainer and has a flange for abutting the seal.