Roller assembly

A roller assembly comprising: a roller housing comprising first and second side walls and first and second end walls forming an enclosure; a carriage assembly comprising a carriage body and at least two carriage wheels rotatably attached to the carriage body, wherein the carriage assembly is located within the enclosure such that the at least two carriage wheels are arranged to protrude from the bottom of the enclosure during use; wherein the carriage body comprises a support portion and at least two concentric pivot points arranged to locate within slanted passages formed in the first and second side walls to allow the carriage body to rotatably pivot about the pivot points; an intermediate adjusting mechanism slidably engaged with the roller housing and arranged to move lengthwise within the enclosure, the intermediate adjusting mechanism comprising a first engagement surface located on an extending member, wherein the extending member extends in a direction substantially perpendicular to the lengthwise movement of the intermediate adjusting mechanism and the first engagement surface is arranged to engage with the support portion; and an adjustment mechanism that passes through an adjustment aperture formed in the first end wall, whereupon movement of the adjustment mechanism the intermediate adjusting mechanism is caused to move lengthwise within the enclosure, wherein the movement of the intermediate adjusting mechanism causes the carriage body to move along the slanted passage.