Just recently acquired a Shimano Dura Ace EX 6 speed hub and was wondering if my shimano MF Z012 freewheel will fit it? If not, can you recommend something on a budget that will work with the 6 speed shimano hub? I'm taking off the freewheel from a 40h Sansin hub and wanted to move it to a 36h hub. Thanks

There are three concerns when matching 6-speed hubs.
1) Are both freewheels in question ISO-threaded? (Probably yes, in this instance.)
2) Are both freewheels standard-spaced, or are both freewheels "ultra"-spaced? (If one is standard and the other is ultra, you may need to adjust wheel dish and axle spacers.)
3) Do both freewheels have low gear (large) cogs within your rear derailleur's capacity?

Yes I believe the MF z012 freewheel is ISP threaded. I don't have any cogs on the shimano dura ace ex hub which is why I wanted to put the MF Z012 freewheel on it but I'm guessing it won't work on the cassette cuz the dura ace uses the spline system and not the threaded system.How do I check if my freewheel is standard spaced? I'm pretty new at this so excuse my ignorance. I will check to see the rear derailleurs capacityASAP. I have a completely stock Miyata 215st if that helps any. Thanks

Sounds like your DA hub takes a 6-speed cassette and what you have is a 6-speed freewheel...no go.
Depending on the year, your hub might have a cassette body that uses an early style "UG" or Ultraglide body where the small cog is threaded and removed with chainwhips, OR you might have a later body that could take either the UG or a later "HG" (Hyperglide) cassette that uses a Shimano lockring.
Once you determine what style goes on your hub, it'll be fairly easy to find 6S HG cassettes, somewhat harder to find the UG, but ask around here if your LBS can't get you one.
If in doubt about what this all means, check out Sheldon Brown's site for explanations.

EDIT: I took my own advice and went to Sheldon's page on DA hubs...he tells us that ALL 6 (and 7) speed DA hubs were UG style AND because they were DA they had an 11 tooth small sprocket which means the DA cassette body has a smaller threaded diameter...if yours matches this description you are going to have a hard time finding a cassette to fit that hub...sorry to say.
https://sheldonbrown.com/dura-ace.html

Thanks for looking that up for me. I just ordered these today from eBay and might cancel the order. Here is the link https://item.mobileweb.ebay.com/viewi...d=221242405943
any recommendations to upgrade to a better system? Should I stay with freewheel or switch to cassette? I wanted to switch from a 40h hub to a 36 because it's getting hard to find rims with 40 holes in 27 x 1 1/4

If you're going to "upgrade", I would go all the way to a new Shimano 105 or Ultegra hub and 8 or 9-speed cassette. If you want to stay freewheel, Ebay is one way:
https://www.ebay.com/itm/Dura-Ace-Hub...-/151063354756

It's hard to tell what you intend with this. If you're modifying the bike for practical use, I would stay away from old Dura-Ace cassette hubs. The cogs for them are becoming hard to find. I would only go that direction for a period-correct restoration.

those are nice vintage hubs, and the price is good, BUT as you see it has the UG style cassette body WITH the stepped-down threaded end for that smaller 11T sprocket. Unless you have a cassette in-hand or know where you can get one, I think you'll actually find it's easier these days to find brand new FREEWHEELS in 5,6, 7 and even 8-speeds (Idon't recommend an 8-S freewheel, however) than one of these (now rare) cassettes.
It's not too hard to find decent 6-S hubs, either 36 or 32 hole, that take a freewheel. Some folks here in C&V might even have some for sale or trade.

Interesting that the pair that Jeff links to above is a Dura-Ace hub, 126 spacing (which is 6-7 speed) and it's clearly for a freewheel...so Sheldon's comment about ALL 6 and 7 speed DA hubs using a UG cassette obviously means just the hubs that take a cassette...some take a FW (and go for $128 a pair!).

You won't have to spend $128 to get hubs that will work well for you

would this be a good alternative>>>>> https://www.ebay.com/itm/Sta-Tru-27X1...item232ac7e23b
or a little on the cheap side? looks like i would need to purchase an quick release axle.

for just a couple bucks LESS, I'd pick this one up from Niagara: better rim (Sun CR-18 is a known and durable brand/model) and better spokes (DT Swiss stainless, not plated steel)...the hub is probably the same or similar.
A QR skewer might even be included...
https://www.niagaracycle.com/categori...d-fw-qr-silver


Edit: If you hunt around on Niagara's site, you'll see they also sell the same 27" wheel you link from that eBay auction, and the price is a couple bucks less. It's actually not a bad rim (Alex AP-18) but I think the SunCR18 is a better rim and a better wheel deal...you decide.

Thanks for the info. yeah I think I'll go with the sun rim.