The blade sits between the two pads in front of the screw. It can be a pain figuring out the right position for the blade but once you get it, it should be much easier. I clamp the blade in the top clamp first then feed it through the work and clamp the bottom by feel. Adjusting the tension on the clamps only takes a small bit of adjusting. When I change blade sizes, say from a #3 to a #5, it only takes about 1/16th of a turn or less.
I'll see if I can get some useable pics later today.
And yes, parts are hard to come by.