locked into the bell by a pair of doors 210 211 shown in their open position in fig2 the doors 210 211 are clamped shut by a clamp mechanism 212 door 211 is mounted on a top hinge plate 213 and door 210 is mounted on a bottom hinge plate 214 for clarity the bottom hinge plate 214 is omitted from fig2 the hinge plates rotate about a hinge pin 215 which is coupled to the bell 203 by a mounting member 216 each door 210 211 is formed with a number of gear teeth 205 which are received in recesses 206 formed in the bell flange 209 as shown in the plan view of fig2 the arms 210 211 each are connected to a respective jaw of a hypergrip system 207 of the kind shown in detail in fig2 the connection is made by approximately ten extended mounting bolts which each carry a pair of springs with the hypergrip system 207 mounted between the springs the system of fig2 and alternative gripping systems are described in detail in wo 01 21933 the contents of which are incorporated herein by reference the system 207 has a pair of jaws 217 218 which are connected to respective hinge plates 219 220 which rotate about the pivot pin 215 the jaws.