Instructions: Serial Numbers for most major products can be found on the instructions in the upper right hand corner.
Tow Bars: Engraved in the metal on the bottom of the driver's side leg.
Brakes: Found on a sticker on the side of the brake.
WD Hitches: In the hitch head between the bar pivots.
5th Wheel Hitches: Engraved on the base of the hitch.