Abstract: Front and rear shields are telescopically joined together. The front shield carries a power driven rotary cutterhead means. Thrust rams are provided between the two shields for pushing the forward shield forwardly relative to the rear shield while the cutterhead means is being operated to mine the tunnel face, and also to pull the rear shield forwardly relative to the front shield. The rear shield includes a gripper assembly for reacting thrust and torque and a plurality of auxiliary thrust rams which extend rearwardly from the rear shield to react against forward end portions of a tunnel lining which is erected under cover of a tail section of the rear shield. A pair of side placed torque cylinders are interconnected between frame portions of the two shields and serve to transmit counter-rotational torque from the cutterhead support of the front shield back to the rear shield.

Abstract: A screwdriver or the like has a shank adapted to hold any one of a number of double ended bits together with a handle for the shank having storage slots for those bits not being held in place by the shank. A split ring, rotatable on the stem of the handle, holds the stored bits against displacement until the ring is rotated to place the space between the ends of the ring into alignment with a selected slot.

Abstract: A main frame includes an annular beam by which the cutterhead is mounted onto an earth boring machine for a rotation about an axis of rotation. A plurality of radial spoke beams extend generally vertically at the front of cutterhead and curve rearwardly to intersect with the annular beam. Each radial spoke beam is constructed from a pair of spaced apart side plate members which define spaces between them for receiving a plurality of roller cutter mounts therebetween. Roller cutters, including gauge cutters, can be installed and removed from their associated cutter mounts from the rear side of the cutterhead. A plurality of generally radially elongate cut-ground-material passageways extend through the cutterhead in the regions between the radial spoke beams.