I was threading a cog on and it never seated, when I got to the point that it should have stopped things got kind of mushy. I knew right away what happened so I gave it a few more turns and it stayed mushy and then got easier an easier and then I was certain what I did. The cog is fine, it threaded right on the other side, no problem.

I am 100% sure that the cog was not cross threaded so that was not the cause. Let me tell you about the wheel:

It is a generic Formula hub with Nashbar branding. it is fixed/fixed.
The wheel is about five years old and has seen all kinds of weather.
I ride it pretty much year round here in Minnesota so it gets coated in salt and other corrosive road chemicals.
The non-drive side stays exposed and when I change cogs I usually will flip the wheel so each side should be equally "worn."
I change the cog a couple of times a year as the weather changes and my tires change.
I have never cross-threaded a cog.
I have never had a cog come loose while I am riding.
I have used cheap cogs. Probably some of the cheapest available.
I use a mix of steel and alloy cogs.
I always use a lot of grease and I am pretty good about getting the threads clean.

It is possible that the exposure to chemicals and various cheap cog changes over time just beat the threads up so badly that they just could not take it anymore? (I've inspected the non-stripped side and it is pretty beat up; I am fairly certain that I will blow it out also if I install the cog on it.) Or is it the case that this should never happened and that I must have done something wrong while changing cogs at some point.

I think you have answered your own question.

You got 5 years beating the hell out of a cheap hub. I'd say you already won. Of course you could gripe loud enough to Nashbar and probably get a replacement.

Cheers to another 5 on the other side!

Since you ride in those harsh salty conditions try anti-seize instead of regular grease. I have seen threads on various parts die during removal of a part that was torqued down and had been ridden in harsh conditions.

Continued installation and removed of parts with cheap threading ain't great too.

There is a chemical reaction that takes place between ferrous steel and aluminum that will occur if you don't use some agent to keep them from coming in direct contact. Salt will displace grease as [MENTION=159729]hairnet[/MENTION] said, and anti-seize compound is a better choice. Also, cheap stamped cogs are often a poor fit and will ruin your hub threads over time. It sounds like it's time to spring for a new hub or wheel.

New wheels are in the mail; I just want to do it right this time.

Thanks for the advice folks - I will get the anti-seize!

Good steel cogs are worth the money if only for the assurance of quality threads that will not damage the hub's threads (assuming the hub also has quality, accurately cut threads). I use Eur-Asian and Dura-Ace cogs exclusively. I make it a practice to start my cogs and lockrings spinning backwards until I feel the thread drop, then start. And do the first several turns with my fingers. For grease, I use trailer hub bearing grease, available at any auto parts store for ~$8/grease *** tube. No road salt is going to touch that stuff; it is designed to handle 4' of submersion into salt water, then be towed at highway speeds.

I am running Miche hubs and frequently change cogs, so each side had probably seen dozens of changes. I often change cogs mid-ride. (I carry a chain whip on the top tube for hilly rides.) On those rides, I may well leave the house on a 17 and 23 on the wheel and a 12 in my tool bag. I have pulled out the cog wrench three times in one ride. And those hubs (I have two fix-fix wheels) seem to be as good as new.

I spent some real money to get started, but the running costs of my set-up are close to zero. $20 chains every 5000 miles or so. I've replaced two cogs (that are just demoted to my winter bike). When the bearings get tired, I pay a local shop $35 to put in new ones. Eventually I will have to replace the chainrings (I alternate between 42 and 43). Maybe in the next 11,000 miles.

This isn't to boast. Just to say that spending some money up front to start with quality threads, then take care of them will pay off over the long haul.) And you get to ride the most pure and elegant machine man has ever invented. (It's rather fun!)

Ben

QFT. I recently opened up a one piece crank set (to strip and repaint the bike) that I had packed 12 years ago. It had never been opened during those 12 years because it always turned smoothly and quietly. When I opened it up, the bearings were still fully packed and the grease was still thick and sticky. That bike doesn't see harsh conditions, but it was still testament to the quality of the salt water marine grease.

Hmm, I've only ever used Park Tool grease for installing cogs. No problems with threads yet, but I've left the 16T and 18T cogs in place for a couple of years now. Wonder if I should invest in some boat trailer grease, too...

This would be good stuff too.

Bel-Ray Assembly Lube | Bel-Ray Company, Inc

Yup grease can last ages... I've removed freewheels and the grease that does not see the light of day was still fresh.
The worst fairing grease is white lithium grease which tends to separate over time leaving a white gunky mess; darn you campagnolo!

it's the ****ty threads, on the ****ty cog, made to ****ty tolerances. this also happened to me w/ a formula hub... and that day happened to be riding a ****ty 15T cog. ****ty cogs aren't case hardened, nor are their threads deburred.

my point is the threads on teh ****ty cog will become subjected to the occassional dirt and debree... the threads will show chipping, warping, etc. the distorted steel threads will cut into the hub's aluminum threads everytime you thread it on.

formula isn't at fault, the cog is the culprit.... be happy it wasn't a nice hub.

p.s. stick w/ eai cogs or dura ace.

Whenever I thread on a freewheel, I always do it by hand. Never any tools. And, I'm quite gentle with it. If it doesn't feel right, I stop and investigate. Perhaps loose cogs are a little different, but it would seem like it would be difficult to do significant damage to one's hub.

I'm voting for the hub just being worn out.