Camper shells (caps, toppers)
The most size-sensitive accessory. A shell sits on the bed rails, so it has to match the rail length, outside rail width and the curve of the bed at the cab and tailgate. Cab height decides how tall a flush-mount shell is. Start with the camper shell swap guide or the compare tool.
Tonneau covers
Soft roll-up, soft or hard folding, retractable, and one-piece hinged covers all attach to the bed rails. Fit depends on bed length, the rail shape and any factory rail system (Ford's BoxLink, Ram's RamBox, Toyota's deck rails). Read our tonneau cover guide.
Bed liners and mats
Drop-in liners and rubber mats are cut for a specific bed, so the generation matters as much as the length: a 2019+ Silverado mat won't lie flat in a 2018. Spray-in liners fit anything, but reduce inside dimensions by about ¼ in per side.
Toolboxes
Crossover (saddle) boxes sit across the rails behind the cab — you need the outside rail width and to know whether your bed has rail caps or stake pockets. In-bed chests and drawer systems need the width between the wheel wells and the depth.
Racks and cargo management
Bed racks clamp to the rails or use stake pockets; drawer systems need the floor length and wheel-well width. Bed dividers and load bars need the maximum inside width.
Tailgates
Tailgate assists, pads and replacement tailgates are specific to generation (and on newer trucks, to the tailgate type — Ford Pro Access, GM MultiPro/Multi-Flex, Ram multifunction).
Have an accessory that fit — or didn't? Submit a fit report.