A threaded fastener such as a weld nut or a weld stud has a projection from a surface thereof, with the projection bearing a thread. According to the invention, a force transmission element is provided in the hollow space of the bottom sillboard. Specifically, a plurality of steps are substantially parallel to the length of the bed, and lead upwardly toward the foot of the bed for easy access to same. Thus, torque transmitted through the friction stack is adjustable by the solenoid. The colored fine resin particles have a structure in which a pigment coated with a water-insoluble resin is encapsulated with a copolymer composed of at least a polymerizable unsaturated monomer and a reactive emulsifier.