Gear Knob I designed for my R34 Skyline. Very Basic, but if you are good at mods in CAD I have included the original files, to add logo's etc as you please. If used to be sold, please give credit. If you need to design a bottom piece to look nicer, you can add a few holes for neodymium magnets into it, so the bottom is self attaching and easy to remove.

"EDIT"

Got around to cleaning up the original a bit for quicker prints. Print the lower at 100% infill and 3 perimeters Print the Gearstick Knob at 80% infill and 5 perimeters. Knob will need supports for the hex nut cutout and a brim of 30 perimeters with a zero offset to ensure it stays stuck, while having the bed at 60 to ensure the bottom doesn't melt. Knob prints ok at 0.2mm layers for the whole thing, but for best results, the first half can be done at 0.2mm layers up to 22mm high, then 0.12mm layers to 42mm high, then 0.08mm layers to finish. It will take around 8 to 10 hours at 50 to 60mm a second.

The lower has a 12mm hole which you can make bigger or smaller depending on your requirements. The 1mm Hex nut cutout will need supports, but can work without them. No brim needed on the lower.

The knob feels great in use, and the texture on the top which is a bit rougher than the bottom gives you good control for gear changes. It lowered my total gear-stick height by about an inch and feels like a short shifter now.

The hole in the base of the knob for the shaft is 9mm wide to allow you to add a thread for a 10mm shaft and even without a correct sized nut for your shaft, it should still hold if you just thread it onto the shaft, but if you have a nut that fits your gear stick shaft, you are guaranteed a solid fit. The nut cutout is 14mm from hex corner to opposite corner. Adjust if needed in 123D Design. Files included.