37 mm Gun M6 (147 rounds) & 3 x .30 caliber (7.62 mm) Browning M1919A4 machine guns (6,750 rounds)
M3 (Stuart I) - 5,811 were built..
M3 with Guiberson diesel engine (Stuart II). 1,285 were built.
M3 with M3A1 turret (Stuart Hybrid)
M3A1 (Stuart III) - 4,621 were built [May 1942 to February 1943]
M3A1 with Guiberson diesel engine (Stuart IV) - 211 were built.
M3A3 (Stuart V) - 3,427 were built.
M5 - Twin Cadillac engines. Redesigned hull. 2,074 were built.
M5A1 (Stuart VI) - M5 with M3A3 turret. The major variant in US units by 1943. 6,810 were built.
M8 - 75mm Howitzer Motor Carriage - based on M5 chassis. The gun was replaced with 75 mm M2/M3 howitzer in open turret and a trailer hook was fitted so an ammunition trailer could be towed. Provided fire support to cavalry reconnaissance squadrons. 1,778 were built between Sep 1942 and Jan 1944.