Just my opinion, but the big knobs on my fixture are unnecessary. Frankly, no knobs are needed. I just pushed the stock by hand as much as I was comfortable with, then turned the jackscrew to hold in place, repeat after some heat dwell time.

Smaller (than my 2") knobs would give a better feel if you elect to push the stock over by turning knobs instead of pushing by hand. Maybe some small plastic ball/knobs?