The first lockstitch sewing machines formed the stitch by passing a reciprocating shuttle carrying a bobbin filled with thread through the loop formed in the upper thread on the off-side of the needle beneath the material. Other methods were soon tried, among these being the rotary hook. This was first developed by Allen B Wilson for which he was granted US patents #8296 Aug 12, 1851 & #9041 june 15, 1852. Wilson formed a partnership with Nathaniel Wheeler to form the Wheeler & Wilson Sewing Machine Co to manufacture the rotary hook sewing machine. In this mechanism a hook picks up the thread from the needle's off-side, carries it around a stationary bobbin to form the lock stitch. The W&W machines along with several other early rotaries used a bobbin which mounted vertically, loading from the end of the machine. The needle normally threaded left to right. On these machines the hook made one revolution for each full stroke (up/down) of the needle. A later development of the rotary was for the hook to be speeded up & make two revolutions for each needle stroke, one while it was up, so a stitch was made on every second revolution of the hook. Other developments were a front loading bobbin & a top loading one with the hook rotating in a horizontal plane. Both of these developments normally used a front to back threading of the needle & allowed for the use of twin or two needles on ZZ models.