Upgrading the turn signals on your Triumph Bonneville? British Customs has engineered Turn Signal Adapter Plates that fill in the oblong holes that are left when switching from stock to aftermarket signals. Each adapter is precision laser cut from aluminum and black anodized to blend with the factory headlight ears. The adapters are designed to fit turn signals with a 10mm mounting shaft. Adapters have been tested with the Triumph Motorcycle Square Turn Signals.