Helmet

1. A helmet for protecting a wearer's head, the helmet comprising:

a) an outer shell comprising a first shell member and a second shell member movable relative to one another in a longitudinal direction of the helmet to adjust a size of a cavity for receiving the wearer's head;

b) an adjustment mechanism configured to control movement of the first shell member and the second shell member relative to one another, the adjustment mechanism comprising:

i) an actuator movable between a first position in which the first shell member and the second shell member are allowed to move relative to one another and a second position in which the first shell member and the second shell member are precluded from moving relative to one another;

ii) two points of attachment between the first shell member and the second shell member, the two points of attachment configured to interconnect the first shell member and the second shell member while allowing the first shell member and the second shell member to move relative to one another when the actuator is in the first position; and

iii) a locking recess on an outer surface of the second shell member;

the actuator comprising a locking projection configured such that, when the cavity is of a first size and the actuator is in the second position, the locking projection extends through the first shell member at a point located between the two points of attachment interconnecting the first shell member and the second shell member and is received by the locking recess to lock the first shell member and the second shell member relative to one another without extending through the second shell member, wherein the locking projection is a first locking projection, the actuator comprising a plurality of locking projections, inclusive of the first locking projection, that extend through the first shell member when the actuator is in the second position, wherein each locking projection of the plurality of locking projections projects away from an inner face of the actuator and is disposed between the two points of attachment interconnecting the first shell member and the second shell member at a different location along the longitudinal direction of the helmet, wherein adjacent ones of the plurality of locking projections are joined at upper ends thereof by a surface that projects away from the inner face of the actuator and extends between the adjacent locking projections in the longitudinal direction of the helmet.

2. The helmet of claim 1 , wherein the plurality of locking projections of the actuator comprises at least three parallel locking projections.

3. The helmet of claim 2 , wherein the locking projections are evenly spaced from one another.

4. The helmet of claim 1 , wherein the second shell member comprises a plurality of locking recesses configured to receive the locking projections.

5. The helmet of claim 1 , wherein a ratio of (i) a distance by which the first locking projection protrudes into the outer shell when the actuator is in the second position to (ii) a width of the helmet is no more than 1:50.

6. The helmet of claim 1 , wherein a distance by which the first locking projection protrudes into the outer shell when the actuator is in the second position is no more than 15 millimeters (mm).

7. The helmet of claim 1 , wherein, when the actuator is in the second position, the first locking projection is hidden from view.

8. The helmet of claim 7 , wherein, when the actuator is in the first position, the first locking projection is visible from an exterior of the helmet.

9. The helmet of claim 1 , wherein the helmet comprises protective padding facing an internal surface of the outer shell, wherein a thickness of a portion of the protective padding in an area of the helmet opposite the actuator when the actuator is in the second position is at least 5 mm.

10. The helmet of claim 9 , wherein a ratio of (i) a thickness of a portion of the protective padding opposite to the actuator when the actuator is in the second position and (ii) a width of the helmet is at least 0.1.

11. The helmet of claim 1 , wherein:

the actuator is a first actuator located on a first side of the helmet;

the two points of attachment between the first shell member and the second shell member are a first two points of attachment located on the first side of the helmet;

the locking recess is a first locking recess on the outer surface of the second shell member on the first side of the helmet, the first two points of attachment configured to interconnect the first shell member and the second shell member and allow the first shell member and the second shell member to move relative to one another when the first actuator is in the first position; and

the adjustment mechanism further comprises:

i) a second actuator located on a second side of the helmet and movable between a first position in which the first shell member and the second shell member are allowed to move relative to one another and a second position in which the first shell member and the second shell member are precluded from moving relative to one another;

ii) a second two points of attachment between the first shell member and the second shell member on the second side of the helmet, the second two points of attachment configured to interconnect the first shell member and the second shell member and allow the first shell member and the second shell member to move relative to one another when the second actuator is in the first position; and

iii) a second locking recess on the outer surface of the second shell member on the second side of the helmet;

the second actuator comprising a locking projection configured such that, when the cavity is of the first size and the second actuator is in the second position, the locking projection on the second actuator extends through the first shell member at a point located between the second two points of attachment interconnecting the first shell member and the second shell member on the second side of the helmet and is received by the second locking recess to lock the first shelf member and the second shell member relative to one another without extending through the second shell member.

12. The helmet of claim 1 , wherein the actuator is pivotally mounted to the outer shell.

13. The helmet of claim 1 , wherein the locking recess is pocketed in the outer surface of the second shell member.

14. The helmet of claim 1 , wherein when the actuator is in the second position, the two points of attachment between the first shell member and the second shell member are covered by the actuator such that the two points of attachment are hidden from view by the actuator when the actuator is in the second position.

15. The helmet of claim 14 , wherein the actuator is received in a recessed region of the first shell member when the actuator is in the second position, wherein the two points of attachment between the first shell member and the second shell member extend through openings in the first shell member located in the recessed region of the first shell member.

16. The helmet of claim 14 wherein when the actuator is in the first position, external end portions of the two points of attachment between the first shell member and the second shell member are visible.

17. The helmet of claim 1 , wherein the locking projection remains fixed in relation to the two points of attachment between the first shell member and the second shell member when the size of the cavity is adjusted to different sizes.

18. A helmet for protecting a wearer's head, the helmet comprising:

a) an outer shell comprising a first shell member and a second shell member movable relative to one another in a longitudinal direction of the helmet to adjust a size of a cavity for receiving the wearer's head;

b) an adjustment mechanism configured to control movement of the first shell member and the second shell member relative to one another, the adjustment mechanism comprising:

i) an actuator movable between a first position in which the first shell member and the second shell member are allowed to move relative to one another and a second position in which the first shell member and the second shell member are precluded from moving relative to one another;

ii) two points of attachment between the first shell member and the second shell member, the two points of attachment configured to interconnect the first shell member and the second shell member while allowing the first shell member and the second shell member to move relative to one another when the actuator is in the first position; and

iii) a locking recess on an outer surface of the second shell member;

the actuator comprising a locking projection configured such that, when the cavity is of a first size and the actuator is in the second position, the locking projection extends through the first shell member at a point located between the two points of attachment interconnecting the first shell member and the second shell member and is received by the locking recess to lock the first shell member and the second shell member relative to one another without extending through the second shell member, wherein the locking projection is a first locking projection, the actuator comprising a plurality of locking projections, inclusive of the first locking projection, that extend through the first shell member when the actuator is in the second position, wherein the plurality of locking projections comprises a second locking projection configured such that, when the cavity is of a second size and the actuator is in the second position, the second locking projection extends through the first shell member at a point located between the two points of attachment interconnecting the first shell member and the second shell member and is received by the locking recess to lock the first shell member and the second shell member relative to one another without extending through the second shell member, wherein the first and second locking projections are joined at upper ends thereof by a surface that projects away from the inner face of the actuator and extends between the first and second locking projections in the longitudinal direction of the helmet.

19. The helmet of claim 18 , wherein when the actuator is in the second position, the two points of attachment between the first shell member and the second shell member are covered by the actuator such that the two points of attachment are hidden from view by the actuator when the actuator is in the second position.

20. The helmet of claim 19 , wherein the actuator is received in a recessed region of the first shell member when the actuator is in the second position, wherein the two points of attachment between the first shell member and the second shell member extend through openings in the first shell member located in the recessed region of the first shell member.

21. The helmet of claim 19 wherein when the actuator is in the first position, external end portions of the two points of attachment between the first shell member and the second shell member are visible.