On my bike, I have my first incarnation of a light flywheel. I made a flywheel holder tool that uses the threaded holes. Since the early (sorta-light) flywheels still had the threaded holes, I was able to use the tool to hold the flywheel while I torqued the mondo nut.
Then, DBM came up with the idea of an ultra-light flywheel, which is so small that the threaded holes get cut away.
I made a bunch of these, and Dave sold them.
Kept a couple for myself. Figured I’d go with the ultra-light if I ever had the left side off again.
I happened to mention to DBM that I was just going to install the nut with a rattle gun.
OH NO!
He says.
Very shallow nut, very easy to make too loose or strip the few threads it has.
He shows me the clever flywheel clamping gizmo he made.
Woof.
I knew he was right.
So, now that there is snow on the ground, and heat in the garage, I decided to make said tool.
Had a chunk of pretty sexy aluminum, some stainless 10mm Allen bolts, and  some time.
Many hours and many chips later, I’m done.
Made a 1/2” square hole for a ratchet or breaker bar. Buggered up the measurements for the corner holes, so it looks a little wonky, but it works.

Right on, Sneeze!
Looks like a Rong Fu. We had one we bought from MSC.

That's a fine To Do board. Good job on the flag.

Dayumm,,
That's okay. I have a suture kit.

It accelerates quicker in the lower gears with the light flywheel. If you are doing a top speed run in high gear then the heavier flywheel has an advantage.

Just like any performance goodie , it gives in advertised area but takes something somewhere else. You just have to try it and see if it’s what you want. I’ve tried 2 reduced weight flywheels and stock. For me , the gains are a interesting experiment, fun stuff , but not enough. I would rather fight it tight corner and have to pull it thru the turn than loose anything from my top end. I’ve spent lots of time and money trying to get my bike in a rpm range that is going to make the best use of it low end torque while still being able to smoothly pull to max rpm and break the ton and maybe then some. A delicate balance between riding style and power output. So I haven’t tried the mini wheel but it performance going the wrong direction for me. I will be putting stocker bag back in. Where some others pile all the performance goodies in their motors yeah it’s fast , but is it fun , is it easy to ride fast as it is slow or does it only have a narrow but very powerful power. A strong Wide power band is easier to ride , you might get me off the line , but watching your  powerband and your cornering , it’s just a matter of studying your riding before you see my butt and tail light go by  just as soon as  your big cam is done making power !

Take your counter balancer out , that will be another 5 lbs easy.
Then it will be a real thumper !

Ouch!