A device for use in physical therapy is provided. The device includes an axis, and a plurality of balls which are rotatably mounted on the axis. Each ball is equipped with a shaft through which the axis extends. The surface of the shaft is equipped with a plurality of spaced apart protrusions, and an adjustable locking feature disposed on the axis that rotatably and releasably engages the grooves formed by the spaces between the protrusions such that the distance between the balls may be adjustably fixed to any of a plurality of predetermined values.