One of the rarest patterns of the SKS is the East German type - the Karabiner-S. Total production quantity is not known, but their survival rate is quite low and most of the examples in the US are Vietnam War bring backs. At any rate, the Karabiner-S is not quite an exact copy of the standard SKS. While it does share all the same mechanical features, the East Germans opted to leave out the butt trap cleaning kit, the cleaning rod, and to cut a German style sling slot in the stock instead of using sling swivels. These differences make the gun relatively easy to spot. Markings are a bit cryptic, with a 2-digit year of production in from of the serial number, followed by a letter prefix and a 4-digit serial number. Not all letters were used as prefixes; in fact only 6 have been documented: A, E, F, L, N, and U. Whether these have specific meaning or if this was a scheme to make production look larger than it really was (akin to the Czech vz.52 pistols) is not clear.