Abstract: A modular helmet system having a helmet base to protect from impacts the crown of a wearer's head and terminating basally in a rear rim and side rims; a C-shaped extension detachably connected to said rims to protect from impacts, when fitted to the helmet base, the base of a wearer's skull; and a crown comb detachably connected centrally over the crown of the helmet base. The helmet base is provided with ventilation windows centrally located over its crown. The comb covers and seals said ventilation windows. The comb is also employed to secure the extension in place, when fitted on the helmet base.

Abstract: A chisel (10) comprises a handle (14), shank (12) and working bit (16). A key (80) slides longitudinally in a dovetail slot (30) and is driven by an actuator sleeve (70) which serves to draw the key (80) up the slot (30). The key (80) has a key-head (82) which engages the blade bit (16) and draws it onto a seat formed a the end of the shank (12). On the other hand, a chisel (10′) comprises a handle (14), a shank (120), and a tool bit (160), wherein the shank is a plastics moulding and the tool bit is moulded on the end of the shank. The shank and handle between them have a selectively disengageable plug (124) and socket (402).