#B Baseplate: The part of the truck the bolts to the deck and attaches to Hanger. The Baseplate contains the pivot cup and the channel for the Kingpin
Bushings: A component of the Truck typically made of urethane that allows for the movement of the Hanger while attached to the Baseplate. Bushings directly affect the handling of the board and are often replaced to achieve a desirable affect on performance.
#C Cup Washer: A component of the Truck that goes between the Bushing and the nut and the Bushing and the Baseplate and allows for the Bushings to be compressed or decompressed for the desired performance characteristics.
#E Enclosure: A box or lid designed to protect your electronics that fastens to the board, often to the bottom of the deck. See also Components Housing.
#K Kingpin: the large bolt that runs through the truck attaching the Hanger to the Baseplate. The kingpin holds the Bushings and Cup Washers in place and keeps them aligned with the Hanger while holding the entire assembly together.
#M M4, M3, etc Metric Screw Sizes: M indicates metric, and the number immediately following it is the diameter of the screw or bolt in millimeters. Course threads are assumed unless otherwise noted, usually. For example, an M4 is a screw or bolt that has a diameter of 4mm and has course threads.
#P Pivot Cup: A urethane or plastic cup that fits into the baseplate and allows for the Hanger to pivot against the baseplate.
#U Urethane: A material for manufacturing skateboard wheels, Bushings, and slide pucks as well as tail guards, side rails, foot stops, and nose guards.