I recently helped someone with his SP-15. One of his problems was that one of the roller height adjustment knobs had broken due to an impact. His press had knobs of solid plastic, sort of pear-shaped with a tapered stem. I installed a replacement knob which was round with a brass threaded insert.
He also had a complaint about the fact that the handle on the crank for manual ink distribution didn’t spin, making turning the crank harder than it could be.
The crank handle was the same type of pear-shaped knob as on the roller height adjustment, and when tightened onto the shoulder screw that passed through the handwheel, it could not swivel. The stem of the knob would tighten against the handwheel.
I swapped this knob with the one I had just installed on the height adjustment (they both have ¼NC20 threads). The brass insert in the knob tightened against the shoulder of the screw and so was free to pivot properly.
So his press (still) had matching knobs on the height adjustment, and a inking crank that swiveled properly. He was ecstatic.
But my question is, was this the wrong knob on the crank to start with? The parts diagram does not show the hand inking mechanism.