These knobs, made of horizontal grain Wenge and finished with Minwax Polycrylic, clear & glossy water-based acrylic finish, have 6 mm pot shaft holes with nut clearance bells, and #5-40 x 3/16” set screws. They run from 0.841” to 0.869” diameter and 0.554” to 0.595” tall. Another knob finished with superglue ended up looking almost pure black, disguising the grain colors. First left as bare wood, the finish of these knobs was dull and lifeless, even though the grain showed clearly. The clear acrylic finish does darken them considerably, but brings out the grain. The bottoms and shaft holes are not coated.
Due to a suspicion that wax finish had been used, these knobs were first washed in ammonia, followed by 91% rubbing alcohol. This leached out some of the natural wood dye, and lightened the wood a bit. In very dark woods, such as Zapote, a soak in denatured alcohol can leach out enough wood dye to reveal grain that would not otherwise be easily seen. The Zapote in mind had for some reason been dyed orange with a protective wax coating.
After soaking and after the first water-based coat, the softer, lighter-colored grain rose and had to be cut and sanded back down. It might have added some interesting texture if left high, but didn’t really look that good. The visible surface cracks are natural grain. The decorative grooves provide a better finger grip.