I replaced the handles on my J&S grinder with something similar to JasonB's ones, the bolts were already there, but the handle bits were past their best.
I used black Delrin and turned it to be a close radial and axial fit on the bolts. I made the ends 1/8" longer than needed to clear the bolt heads and turned an internal 7.5° per-side taper in them, with the small bit at the outside. I then turned up plugs with a matching taper and the same dimensions.
Very gentle 70-80°C heating in the oven expanded the handles (on the bolts) to the point where the end caps just popped in with finger pressure.
Being Delrin, they turn smoothly and feel pleasant to the hands.