surface thereof is substantially in contact with the mandrel 34 and substantially the entire length of the exterior surface thereof is in contact with the latch sub housing in this position of the latch member 84 u2032 it will be understood that there is limited room for radial expansion of the latch member 84 u2032 and accordingly a greater axial force must be applied to the mandrel 34 in order to press the ridges 96 98 100 provided thereon past the ridges 90 92 94 provided on the latch member 84 u2032 the aforementioned ridges of the modified latch sub 80 u2032 are of the similar size shape and spacing as those of the latch sub 80 shown in fig2 and 3 however the axial force required to pass the mandrel 34 downhole and thereby activate the swivel joint assembly may be reduced by retaining the latch member 84 u2032 in a more uphole position within the latch sub housing in this way the latch member 84 u2032 is located in a region where the radial dimension of the annulus between the latch sub housing and the mandrel 34 is increased the latch member 84 u2032 is therefore provided with increased room for radial expansion and accordingly may be radially expanded more readily upon the application of downhole axial force to the mandrel 34 the axial position of the latch member 84.