The threshold plate, also referred to as a tread plate or sill plate, fits across the door sill aperture at the point where the occupant steps in and out of the car. The sill top surface is a vulnerable area, as the paint along the top is worn through remarkably quickly by repeated foot contact, exposing bare metal that corrodes rapidly once the protective layer is broken. On the MGB, sill tread plates were introduced as standard fitment from the 1970 model year, added at the base of the door openings as part of the interior and exterior changes that accompanied the new seats, dipping mirror, and Rostyle wheels, and prior to 1970 the unprotected sill step frequently shows paint loss and scuffing. The same plates fitted to the MGB Mark II are used on the MGC.
Materials & Styles
Threshold plates are manufactured from hard-wearing mirror-finished stainless steel or chrome, providing a surface highly resistant to scuffing and straightforward to keep clean. A range of styles is available, including plain stainless and lettered versions in MG, MGB, and MGB GT inscriptions, alongside the original alloy style for owners restoring to period-correct specification. Chrome-plated plates provide a bright, traditional appearance matching the original specification, while stainless steel alternatives offer improved corrosion resistance for cars regularly driven in wet conditions, maintaining their finish without surface treatment where chrome can pit and flake as the base metal corrodes.
Fitting
Threshold plates sit alongside the stainless oversills in protecting the lower body at the door aperture and are particularly effective on a car that has had new or freshly painted sills, where protecting the finish from the first day of use is the obvious priority. They should be fitted after paintwork is complete, using a thin bead of sealant beneath the plate to prevent moisture being trapped between the plate and the painted sill surface, as trapped moisture accelerates corrosion unseen beneath the plate, undermining the very protection the plate is intended to provide. Screw holes should be pre-drilled carefully to avoid penetrating the inner sill structure, and on cars where the sills have been replaced, checking alignment with the door seal and shut line before drilling ensures a neat finish. Threshold plates are available individually or as a pair, with all fixings included.