for all locking segments at the same axial position assuming the locking surfaces on each of two locking rods were spaced 0 100 34 apart each locking surface on one rod could be spaced axially between the locking surfaces on the other rod which would then allow the locking segments to lock with one of the rods at 0 050 34 increments in a preferred embodiment of the invention four locking rods and four locking segments are provided the axial position of the locking grooves on two diametrically opposed locking rods are identical while the other two diametrically opposed rods have axially offset locking surfaces high seal squeeze is thus obtained by the ram blocks although the application of high axially directed opening forces applied to the ram shaft 24 does not tend to tilt the piston 30 within the cylinder 46 the same result could be obtained by offsetting the axial position of the mating surfaces on the locking segments while corresponding locking surfaces on the rods remained at the same axial position the multiplicity of locking grooves are preferably provided along a relatively long axial length of each of the rods 42 or 142 preferably the grooves extend over a length of at least 45 of the nominal diameter of the passageway 14 through the bop body this feature allows different ram blocks to be attached to the ram shaft of each actuator so that locking will be effected over a.