spring-beam

from The Century Dictionary.

• noun A beam reaching across a wide space, without a central support.
• noun In ship-building, a fore-and-aft timber uniting the outer ends of the paddle-box beams, and carrying the outboard shaft-bearing.
• noun An elastic bar at the top of a tilt-hammer jig-saw, or mortising-machine, to accelerate the fall, or afford return motion.
• noun In a railroad-car, one of two heavy timbers resting on the springs of a six-wheel car-truck, and serving to support the bolster-bridges, which, through the bolster, support the car-body.
• noun In carpentry, the tie-beam of a truss.