What about filling it with JB Weld or a similar 2-part putty, drilling it and tapping it? I'd try something softer than a steel JP Weld, such as a 2-part wood filler, such as Quik-wood epoxy
You would only use a small portion and mine has lasted for many years.
To make the drilling and tapping easier, you could insert a 5/16 bolt coated in light grease as a release agent.
Practice with a 5/8" nut before committing to the shift knob.

Maybe you could take either or both parts to a machinist and have them re-tap one part or the other to make them fit.

I don't think it would be terribly expensive, but it depends how much you like what you have now. (i.e. just a whim to make something you've got usable, or you really like what you have and really want to make it work.)

I should have made a list of the suppliers I already tried, but anyway McMaster was the first, they dont have 5/8 to 5/16. Apparently this is not a common size.

In the USA, here's one place to order them:

thread reducers | McMaster-Carr

hey let's resurrect an old thread.  I was getting ready to toss out a stripped Mini shift knob and decided to save it.  I drilled out the rubber insert and found a 5/8" UNC bolt screws right in.  So I went searching for a thread reducer from 5/8" UNC to  5/16" UNC and I cant find one.  This annoys me to the point where I might drill and tap the 5/8 bolt and make my own insert.  But hey, they made a zillion of these, somebody has to have thread-reducing inserts.  Any clues?

i always watch the Red & Green Show, they do topnotch shift knobs and tons of other things under the sun.

I always wondered how they could work a sphere on a manual lathe, like a staircase bannister finial.  Turns out (pun) that they cut out a circular pattern and jigged it above the workpiece, and then shone a bright light down on it, then cut to the shadow.  Duhh.  I mean to try it someday when nobody is around to watch me mess it up.  

if you want to try making plastic shift knobs, there was a good how-to in Rod & Custom magazine.  But it was in the May, 1968 issue...

Quite poetic Triggerboy but did you notice Richard1 used a lathe.

Not as creative as Richard's shift knob, but the one in my Mini has just as much sentiment. It is the original procelain front door knob from the first house my wife and I purchased and spent 10 years in a live-in renovation. The house was originally built about 1901, so the knob is coming up to about 115 years old. Having big hands, most shift knobs feel small and wimpy, but this one fits perfectly and has that soft, almost "old English white" colour of old porelain. It is the most cherished part of my Mini.

Thanks for the comment. As you may have seen, I've salvaged a lot.

In this case there is a personal note too, as my granddaughter used to spend hours in that tree since she was a couple of years old. Not only picking the walnuts, but just sitting and admiring the trees and fruit around her. She is now 10 years old, and knows that some day this Mini will be hers. So she will be driving with a piece of her tree.

 

i just can't help not to comment on this thread, i want to commend Richard for such a wonderful creation, i always like people who can create something out of almost trash. i dislike people who always buy expensive parts even though the old parts are still use-able.  i know as mentioned on other replies that richard was not the only one who does shift knobs,there were even names mentioned, yes of course, BUT others would get their wood from Lowes or Home depos and cost some dollars for kiln dried wood whatever, and here's a guy who utilizes what's in the backyard, a fallen tree,..can't get better than that. 

thanks for the idea sir Richard....hope this serves as a wake up call to those who are great spenders, to tone it down and be practical, quit being a "money know how" guy....times are hard

 

till next time....

Interesting thread. Making shift knobs was a hobby of mine in high school, only I was working with soft metals. Strange you bring up Bob's Knobs. I recently visited with Bob and his wife. As I was leaving Bob handed me a box and told me this is the last of Bob's knobs. His wife walked over opened the box reached in grabbed a knob and said thank you. I have the rest and will sell them on if anyone is interested. If you did not see Bob at this years MM east I'm not sure he will be attending any more meets. I also have a freshly built 1300 GT block built with Cooper S parts that was ear marked for one of Bob's projects. I have it at my shop in Hampton Va. Bob had over $7000. in the power unit with remote Cooper S tranny, Hardy Spicer drives and remote shifter. If interested the first $6200. can see it run on test stand and take it home. Contact me if more info is required. Understand this is not a core for rebuild but a spare no expense build with new parts and balance , bore, head work all surfaces machined. Steve (CTR)

Nice.

Nice work. You're not the only one making knobs. I made some and so did Bobb. Bobb's knobs wre given to all the participants in the 2014 Can-Am Challenge.  The first picture shows my knobs, the second is Bobb's knobs.

Fantastic job!

Beautiful job Rich! So nice how the grain in the wood displays too. Kind of reminds me of a beautiful agate. No two alike. Great job! Thanks for sharing!

Mini Estate

Nice work Richard.

Looks great!   Nice Job!

Today was the day. I went over to a friend's house with my piece of walnut from my dead tree. I hedn't used a lathe since 1963, but that didn't stop me. A few hours of work and this is what I have for my pickup.