Subaru Shift Knob (Custom Weighted)

I designed this shift knob for my Subaru, because I wanted something that was weighted (for 'easier' shifting); the standard shift knob was only 196g, and that simply wouldn't do. Thus, I found a cylinder of lead that was lying around and fitted it into the center of the design, which brought the weight up to a hefty 512g.

Although this design is highly specific, perhaps someone can use all or part of it to improve theirs.

Hardware needed:
(1x) M12x1.25 standard or Nyloc nut (for the actual shifter shaft)
(8x) M3x35 bolts (for attaching the two halves of the knob together)
(8x) M3 standard nuts (function as embedded nuts to keep the halves secure)

After installing it, my shifts have become slightly smoother and even after sitting in the sun all day it hasn't lost its rigidity.

UPDATE: (2017-08-14) Still shifting wonderfully and has survived a few 40C days in the sun; a testament to PETG's temperature tolerance...