Abstract: A method of locking a surfboard to a roof rack crossbar using a series of adjustable mount block assemblies (10a-b) affixed to the rack crossbars (13) at a lateral position of contact with the sides of a surfboard (15a-b) placed horizontally on top of the crossbars. The mount block assemblies utilize a metal clamp (12) that is vertically adjusted to the thickness of the surfboard at the lateral position of contact. An internal axle (14) connects two side cams (10b) vertically adjacent to a center mount block (10a) with clamp (12) affixed within the side cams. Axle (14) allows for the clamp assemblies to open and close by means of rotation of the side cams relative to the position of the mount block. The mount block assemblies utilize a lock pin (16a-b) that inserts through an alignment of holes in the mount block assembly to a position of engagement with a cam lock assembly (22a-f). Utility of the cam lock serves to prevent or allow removal of the lock pin.