Yeah, lets see something that may actually be worth knowing on ET for a change. It's been 145,877 posts since that happened.
AutoEx is an electronic order that bypasses the specialist and is filled instantly. There are some rules though. There has to be at least 200 shares displayed on the quote size for it to go through, your order has to be at least 100 shares and no more than 1099 shares, and the specialist has to have this feature turned on or it won't go through. Also when it does go through it will only take the size displayed for example: XYZ last traded 50.05, the quote is 50.00 x 50.10, the size is 8x1... in this scenario i can autoex the bid and if my order is for 1k shares at a limit of 50.00 then i will get filled on 800 shares instantly and the remaining 200 will be routed to the specialist. I can not autoex the offer here because it has to be a minimum 200 shares displayed and this example only shows 100 on the offer. Sometimes when there is increased volatility in a stock the specialist will turn the autoex feature off to keep the stock from getting too wacky. Hope that helps.