I know this has been done before, but I never tired it myself, it is so easy, I'm kicking myself for getting rid of all the parts w/o the knob thinking they were junk, or it'd be a pain in the butt to try to fix them.
I don't hate rubber strap accessories anymore, follow my 12 step plan and you too can be cured!
So easy, and cheap, even if you don't have the tools, they are cheap enough and you'll use them again.
I'm still looking for broken ones to repair.
First what you'll need
1 broken knob rifle, binocs.....
2 Michael's crafts ball head common pins 350 for $4.99 multi colored, but easily painted
2.5 Braided elastic from Michaels, Joann, etc for strap when pin is fixed
3 pin vise, dremel, or in my case cheapo Harbor Freight rotary tool $7.99 on sale
4 Drill bit, 0.020" or 0.025". Included in Harbor F. 30 piece mini drill set #94606 #3.99???
5 Method of securing rifle in place for drilling, I use a HF screw on mini table vise.
6 Super glue, epoxy, whatever you prefer
What to do!
7 secure part for drilling
8 set center for drilling, I usu a very sharp knife and give it a little twist to set center, drill 1/8 hole 0.125", or less depending on item being repaired.
9 Cut pin down to fit into drilled hole, start too long and cut til it is about 1/32 off base of part, need to leave some room for the strap.
10 super glue pin in place
11 Take a second to admire your work, so far!
12 Once glue is dry, and pin is set, pop on existing rubber strap. Done, like new!
12A alternate method if you don't have the rubber strap!
Take a length of 1/8 braided elastic, fold it over itself about 1/8", and snip a very small hole in the center of the 4 elastic strips, tight enough to fit over the pin head, do same for other end leaving desired length for your new strap. Pop the new strap onto the knobs/pins, and you're done, See pic with braided strap!
12B if you choose to use the braided elastic strap method, don't forget to hit the ends with a lighter or something to keep it from unraveling!
I know it sounds like a lot of work, but I can do 1 rifle in less than 5 minutes. The end result is clearly worth the effort.
Hope some guys will give it a go.