This is my first foray into the world of syncro shifters and 7 speed freewheels. I have 2 Dura Ace 7-speed freewheels, 12-24 and 13-26. I am trying to build a 12-28 or 29. The larger cogs are proving difficult to find. I'm wondering if 6 speed uniglide cogs will work.

I have read that some of the 6 speed cogs have integral spacers and am aware that those will not substitute properly for 7 speed because of the different spacing.

So here are my questions:
-Are the inside diameters and spline patterns the same between 6 speed and 7 speed?
-Are the cog thicknesses the same?
-When I find a used 6-speed freewheel that I am considering scavenging for parts how can I tell if it has integral spacers or separate spacers? (assuming that I am buying on BF or ebay where I can not easily inspect or disassemble it)
-Is the difference between the 6-speed freewheel and the 7 that the 6 speed has only the 2 largest cogs in the larger diameter spline while the 7 speed has 3?

Any other suggestions or helpful advice?
The cogs I'm looking for are:
16t and 18t in positions 3 and 4.
28t in position 7. (or 25t and 29t in positions 6 and 7)

Thanks,
Brent

Money overflows in SF bay, buy stuff Try things .

Yes.
For splined cogs, yes.
Except for the 14t (IIRC), all of the splined cogs have separate spacers.
No. On the 6-speed, there is one threaded cog, 2 small-splined cogs, and 3 large-splined cogs. On the 7-speed, the smallest cog threads to internal threads on body while the second-smallest threads onto external threads. The splined cog arrangement is the same except the spacers are thinner on the 7-speed.


Customizing Shimano freewheels is quite easy compared to the SunTour Winner/New Winner units. I must have done a couple hundred when I worked at Euro-Asia Imports, which offered customized freewheels for its customers. I think I remember putting together a couple 12-32 7-speeds, using 600EX cogs for the largest. I don't think there was a 29t for the large spline- it jumped from 28 to 30.

Euro-Asia probably still has the old cogs sitting in boxes somewhere. However, they only only sell to dealers and tend to be quite expensive. Loose Screws lists a couple Shimano freewheel cogs, also:
https://www.loosescrews.com/product-...-cogs/page/14/

Loose screws is selling a 14-28 6 speed

https://www.loosescrews.com/product/...6-18-21-24-28/

I just picked up 2 - 57% off sale now (spectular57 discount code as i recall)

There's a sepatate thread from yesterday on the discount

On th 6 the first cog threaded, next 2 small spline, last 3 large spline

Thanks to all of you!
That is exactly what I wanted to know.
Brent