Abstract: Two designs for a spring-loaded roller mechanism (154a and 154) having monocoque and semi-monocoque characteristics. The monocoque design uses a single tube for both roller and axle (226), thus it carries most of the rotational stress. A pair of mounting plates (209) at either end serve multiple functions. They hold the assembly to a base surface, they serve as end caps for both a housing and the roller itself, they serve as the spindle around which the roller rotates, and either one can hold one end of a coil spring (166a). The other end of the spring attaches to the roller through a slot. Thus, the roller can be rotated around the mounting plates using the biasing force of the spring. The semi-monocoque design uses two tubes. One of them, an inner tube, slides into another, or outer tube. The outer tube is the roller. One end is open, the other closed. The open end allows the inner tube to slide into it. The closed end is circular allowing it to rotate within a holder. The inner tube serves as an axle.