Originally Posted by jennandjuicetm
I tried to Google what a Jack is but got mostly nowhere. My guess would be extra support. Can you explain further?
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You are correct; a jack stud is a weight bearing, supporting stud. If you refer to the first image in the following link, it will display a jack stud (along with a king stud and cripple stud) within the framing structure of a window: http://www.do-it-yourself-help.com/f..._a_window.html
Basically, use wood to bear the weight rather than relying on fasters (nails/screws). I am not saying not to use fasteners, just don't use them to support the weight. Hope that makes sense.