The model range for which Seagull is most famous is the "Classic" range. These "square block models" comprised the 64 cc Featherweight (aka Forty Minus) and Forty Plus, and the 102 cc Century and Century Plus. The Forty Minus and Plus used identical power units, but the Plus had a larger gearbox and propeller. The Century and Century Plus used even larger gearboxes and propellers. Classic model engines were produced from the late 1950s until the mid-1990s, and many examples are still in everyday use. The long life span is down to the high quality metals and the use of high-tensile bolts and studs.