assembly 40 urges the tapered locking ring outwards against the tapered load shoulder 58 on the hanger 50 and into engagement with the landing groove 9 in the surface wellhead 4 at this point further longitudinal movement of the second tubular assembly 40 is prevented the engagement of the engagement assembly 54 with the shoulder 8 and groove 9 in the surface wellhead is shown in the right hand portion of fig1 a and 2 a the supply of hydraulic fluid to the piston cavity 114 is maintained causing the piston 116 to continue its longitudinal movement towards the casing string 6 with the engagement assembly 54 restraining further movement of the second tubular assembly 40 further movement of the piston 116 applies tension to the inner sleeve 42 at a given applied tension the shear pin 86 retaining the tensioning collar 78 shears allowing the tensioning collar 78 to move longitudinally with respect to the inner sleeve 42 this in turn releases the locking ring 72 from the groove 74 the bias of the locking ring 72 urges it into engagement with the corresponding groove 24 in the inner surface of the outer sleeve 14 this position is shown in the right hand portion of fig2 a and 2 b at this point the casing string 6 is secured and held under tension further tension may be applied by increasing the pressure of the hydraulic fluid in the piston cavity 114 forcing the piston further towards the casing string 6 as noted above the grooves 24 and the corresponding lands in the inner surface of the outer sleeve 14 are formed to allow the locking ring 72 to move longitudinally towards the casing string 6 as further tension is applied to the outer.