111W

The way you are threading your machine is correct. The red line path is incorrect and is not a special threading pathway for heavy material. Luckily for Conner Sewing, 16 class machines are very forgiving. As a side note, I have a 16K113 in front of me at the moment.

Overall length of the 126x11 varies with needle size as the length of the eye and length of the point increase as the needle size goes up. I do not have the range of variance. The dimension from the furthest end of the shank to where you first come to the eye is 1.850" (47mm). Measured in the same manner, dimensions are 44.5mm (1.751") for system 190R and 1.530" (38.9mm) for system 135x17.

On the 111W117 there is a clamp atop the extended lifting presser foot bar as dikman has indicated. Attached to that clamp would have been an extension that goes down in front of the machine and rests at an angle on a sliding collar. The collar is on the on the upper thread tension post where the adjusting thumb nut would normally be. As the thickness of the material increases, the angled extension rises and begins to relieve pressure on the beehive tension spring. Upper thread tension is reduced. The lifting presser bar has a flat spring as most 111W machines do, though of a different part number than other flat springs as it has attachment points. There is an auxiliary bowed spring attached atop the main spring and this auxiliary spring is extremely light. The adjusting thumb nut is shorter than in other 111W versions to allow for the bowed spring. All or almost all foot pressure comes from this extra light auxiliary spring. In its intended use for stitching sleeves in coats, the mechanism functions to allow maximum fullness in the thick padded portions, so that the stitches do not compress the padding. The resultant stitch in thick padded portions would be somewhat close to a basting stitch as the bobbin thread would only be drawn slightly into the material.