During the Cold War, the Soviet Union shared the SKS design and manufacturing details with its allies, and as a result, many variants of the SKS exist. Some variants use gas port controls, flip-up night sights, and prominent, muzzle-mounted grenade launchers (Yugoslav M59/66, possibly North Korean Type 63). In total, SKS rifles were manufactured by the Soviet Union, China, Yugoslavia, Albania, North Korea, North Vietnam, East Germany (Kar. S) and (Model 56) in Romania. Physically, all are very similar, although the NATO-specification 22mm grenade launcher of the Yugoslav version, and the more encompassing stock of the Albanian version are visually distinctive. Many smaller parts, most notably the sights and charging handles, were unique to different national production runs. A small quantity of SKS carbines manufactured in 1955–56 was produced in China with Russian parts, presumably as part of a technology sharing arrangement. The vast majority of Yugoslav M59 and M59/66s have elm, walnut and beech stocks. Russian SKS's had stocks of Arctic Birch (or "Russian Birch"), and the Chinese were of Catalpa wood ("Chu wood").