Reply to stop point in the middle of knob?

I have changed the original tsi from ean and i made a xone eq and i set the filter at the gain knob.
My problem is that the gain knob hasn't a point where the knob stop(like the eqs have in the middle),and is a little difficult to find the point where filter getting off.
Does anyone knows if we could make these gain knobs like others?
I tried to find how these knobs stop in the middle,but i didn't find it.