A kit of parts consisting of: an optical fibre connector system ; an "O" ring ; and a housing comprising an opening and a wall ; an optical fibre connector system comprising: an adapter comprising an adapter body with a first locking component ; the adapter body possessing a ring-shaped raised edge surrounding and extending from one end of the adapter body , the ring-shaped raised edge possessing a first connecting surface ; and a locking ring , the locking ring being constructed such that it can be installed around the adapter body said locking ring possessing a second connecting surface and a second locking component ; wherein when the adapter body is inserted into the housing wall via the opening , the "O" ring is positioned between the first connecting surface and the surface of the wall ; the second locking component being constructed such that by partially rotating the locking ring relative to the adapter body brings the second locking component into contact with the first locking component resulting in the positioning of the first connecting surface at a pre-set distance from the second connecting surface ; the pre-set distance corresponding to a distance for compressing the "O" ring between the first connecting surface and the housing wall positioned between the first connecting surface and the second connecting surface; said first locking component and said second locking component being constructed such that they connect together when said locking ring is rotated by an angle of 90 degrees or less than 90 degrees relative to the adapter body, thus allowing positioning of the first connecting surface at the pre-set distance from the second connecting surface. an optical fibre connector system ; an "O" ring ; and a housing comprising an opening and a wall ; an optical fibre connector system comprising: an adapter comprising an adapter body with a first locking component ; the adapter body possessing a ring-shaped raised edge surrounding and extending from one end of the adapter body , the ring-shaped raised edge possessing a first connecting surface ; and a locking ring , the locking ring being constructed such that it can be installed around the adapter body said locking ring possessing a second connecting surface and a second locking component ; wherein when the adapter body is inserted into the housing wall via the opening , the "O" ring is positioned between the first connecting surface and the surface of the wall ; the second locking component being constructed such that by partially rotating the locking ring relative to the adapter body brings the second locking component into contact with the first locking component resulting in the positioning of the first connecting surface at a pre-set distance from the second connecting surface ; the pre-set distance corresponding to a distance for compressing the "O" ring between the first connecting surface and the housing wall positioned between the first connecting surface and the second connecting surface; said first locking component and said second locking component being constructed such that they connect together when said locking ring is rotated by an angle of 90 degrees or less than 90 degrees relative to the adapter body, thus allowing positioning of the first connecting surface at the pre-set distance from the second connecting surface. <EOS>