Swiss SIG 551 2-position. Gas Regulator in used in like new to new condition. This item along with other items are very hard to find, and can be used for both a SIG 551 and 556. The 2 positions include normal setting and "adverse conditions". This is perfect to replace a worn, lost, or damaged part, or it can be modified to make a 4-position gas regulator for off and suppressed use. All SIG 551 parts are becoming increasingly unavailable, so grab one now while in stock!