Yes. The original receivers made for the military ( select fire ), Had the notch in the middle of the op rod rail. This notch is dual purpose. It is a detent housing of sorts for the small nipple or protrusion on the inside of the connector arm assembly, to limit front and back travel and keep it equidistant from receiver right surface, and it is to facilitate assembly and disassembly of the op rod. On SAI receivers, they left the factory with a standard civilian type, rear take down op rod notch, then were sent to Rock Island to have the middle notch cut in them and full auto conversion done, hence two take down notches. You could actually do a conversion without the middle notch, but you would have to grind off the nipple or detent from the connector arm......and do about 25 years for it. Freakin psychopath politicians. They think their opinions are the word of god. That is what the law is, the "opinions" of legislators (lawyers), of how you should live your life. I simply refer to them as jackasses. I think they forgot we are free and have all the freedoms our forefathers fought and died for. Like, the right to bear arms. It doesn't say what kind of arms on purpose. What their law does say, is that a badge does not grant extra rights in this country....therefore, if a cop can carry a machinegun in his cruiser, so can we. Their law also says that the constitution must be interpreted as it was meant then, now. You cannot change it's meaning to suit yourself today.....Hence my terminology for them,...jackasses. Sorry for the history and law lesson speach.... just went through a bunch of crap with the agent in our area at the shop. He is big on opinions, and no facts or laws to back it up. Off my soap box now. Venting complete.