How to choose the right plumbing fitting

Start by identifying exactly which fitting has failed rather than guessing from the symptom. A dripping tap is usually a worn washer or cartridge inside the tap body, not the cock or isolation valve behind it. A cover plate that won't sit flush is often the wrong diameter for the pipe or wall box, not a fault with the tap itself. If you're unsure, remove the worn part and bring it (or a clear photo with a ruler for scale) as a reference, since thread sizes and hole spacings vary between brands and eras of plumbing.

Finish matters as much as function in a bathroom or laundry that's otherwise finished in chrome, matte black or brushed gold. Mixing finishes on visible fittings, even slightly different shades of chrome, is one of the most common reasons a replacement looks out of place. Where a part sits behind a vanity or inside a wall cavity and won't be seen, function and fit take priority over finish. For anything touching the main water supply or requiring pipework to be cut or moved, engage a licensed plumber rather than DIY-ing the job.