Size adjustable helmet

A helmet comprising:

• a front shell,
• a rear shell movable in the forward-rearward direction with respect to the front shell,
• portions of the two shells overlapping each other and presenting mating surfaces with interengageable protuberances which can engage each other to retain the shells in a given overlapping position, and can disengage to allow the shells to change their relative position,
• and cam means for selectively (a) holding the mating surfaces in engagement, and (b) releasing them to disengage, the cam means including two cam members recessed into two recesses on either side of the said portion which lies outwardly of the other, each cam member being swivelable about an axis which is retrained with respect to the inwardly lying mating surface, each cam member being adapted to urge the two mating surfaces into engagement, each cam member being integral with a cam-operating lever which is accessible from the exterior of the helmet and by which the cam member can be rotated about its respective axis, each said lever being wholly recessed into the recess of its respective cam member when the latter is urging the two mating surfaces into engagement, each said lever being swingable to a position in which it extends generally outwardly away from the helmet, in which position the cam member releases the mating surfaces.