Wondering if the cogs on the new style Shimano freewheels with the lockring will fit on an old Shimano 600 or Dura Ace freewheel body. I am thinking of disassembling a new freewheel to use the inner cogs to fill in worn cogs and keep an old freewheel body on the road. If they do fit, I assume I would have to use the outer threaded cog to hold it together. I also expect there would be shifting differences with mixing old and hyperglide cogs, but I am friction shifting so ok with that.

Your terminology is confusing. You want to transplant cogs from a shimano _cassette_ onto .... something?

Cogs from new Shimano freewheel where it is held together by a lockring (MF-HG37) - onto an old Shimano 600 freewheel body where the last cog threads on to hold it together. No cassette involved.

OK, assuming that the cogs of the MF-HG37 have an identical spline pattern as the MF-HG40:
https://techdocs.shimano.com/media/te...9830609020.pdf
I'd say your plan will work. The splines look identical to the old 600/Dura-Ace freewheels I worked on (20 years ago).

FWIW: Loose Screws still sells individual Shimano freewheel cogs:
https://www.loosescrews.com/index.cgi...ogs&tc=Shimano
Judging by the prices, though, it's probably cheaper to buy a whole new Shimano freewheel.

Thanks- I had not found that tech document - the body does look the same as the old ones. I have looked at Loose Screws but I thought the new tooth designs would shift better. I may give one a try.

Why don't you use the new freewheel if you want better shifting?

You'll also have to keep the top threaded-cog on the 600/Dura-ace freewheel since there's no way to attach the top cog from the Hyperglide freewheel as the body on those older freewheels are threaded in that position. If your Dura-ace freewheel is 7-spd, you'll have to retain the 1st two cogs as they are threaded.

It also depends on how thick the cogs themselves are.

In case anyone is interested, I did buy and try one of the freewheels mentioned above to see if the cogs fit an old body. It appears that they do not. The cogs have the proper diameter but the spline pattern is slightly different. The new cogs have one 'square' spline that is used to locate the cogs relative to one another. I did not check into grinding off the square spline.

In addition to the silver cog freewheels with the lockring to hold them together, I also found a later model Shimano freewheel with brown cogs and the small cog threads on to hold it together. These are not even close. The freewheel body is all one diameter (in between the small and large of the old style body) and the last 3 cogs are pinned together and only the small one of the three is splined and contacting the body.

I knew from the defunct bikepro.com site that the HG freewheel bodies are different: https://www.bikepro.com/products/freewheels/shimfw.shtml
This is from that site about the HG-20:"The inner notches on these cogs, is not compatible with any other Shimano made cog."
Someone posted a pic of a modified MF-7400:

Zombie thread. Note that my (previous) posting is almost 5 years old.