The classic Monza quick opening gas caps were almost universally used on racing machines of the 1950s to 1970s. Suitable for the Bonneville, T100, Thruxton, and Scrambler. It fits also the Adventurer and Thunderbird. The adaptor is machined to fit the Bonneville gas tank and to protect it from peeling too. The cap comes in polished alloy. Bolt on installation.