The tubular housing of the fixture has a coarse external thread (2) which is chamfered at the end and which extends over the whole length of the tube. The housing has three recesses (9) at the top of its bore with which a spanner key can be made to engage. The key is used to screw the housing into a chamfered hole (14) in a support plate (13) which is mounted below ground and which is made from a plastics material which can be recycled. A lid (10) incorporates a hinge pin (11) which is captive in a hole (8) in a lug in the bore of the housing.
