top section of each well casing usually includes a coupling which is threaded over the top end of the casing section for connection into the housing 11 some casing sections are equipped with a long coupling 25a and other sections will have a short coupling 25b at the top end the coupling structure for connecting into a long coupling 25a is illustrated in fig1 the several parts of the connecting structure include a make up cap 26 an upper wedge ring 27 lower wedge ring 28 and a retainer member 29 when the long coupling connection is made a boss member 27a on ring 27 rides in an inclined slot 30 at the bottom end of plug housing 11 this arrangement allows the front face of ring 27 to wedge against the long coupling 25a wedge ring 27 also has a retainer spring not numbered which seats in the wedge ring and encloses the long coupling 25a the lower wedge ring 28 also includes a boss member 28a this boss member rides in an inclined slot 29a in the retainer member 29 when cap 26 is threaded onto housing 11 the top face of ring 28 wedges against the bottom face of ring 27 and also against the lip of coupling 25a the wedge ring 28 also has a retainer spring not numbered seated within the wedge ring and enclosing the long coupling 25a in addition a flat ring 31 is seated in a groove in cap 26 when the connection is made ring 31 bears against the top face of the retainer member 29 thus providing a hold down means for the retainer member a set of seals 32 provide a fluid tight seal between the lower end of housing.