Hi All,
I am currently building two bikes and have installed two Shimano UN55 bottom brackets.
(These are the traditional square-taper cartridge bottom brackets.)

It struck me that the white anti-seize paste that was applied by the manufacturer on the thread was only applied on one of the two threads:
It was only applied onto the thread that is solidly attached to the actual cartridge,
and none was applied to the thread of the cup that holds the cartridge at the other end.

Would anybody of you know the reason why it makes sense to apply anti-seize paste only on one side?

By the way: The UN55 bottom bracket that I am talking about is not the type where of the threads is a "plastic" thread:
Both threads of the UN55 are made of metal.
I.e. I am talking about this type:
https://www.jensonusa.com/!aE06wbcdOc...Bottom-Bracket
...and not this type:
https://www.nashbar.com/bikes/Product...&top_category=

The right side (drive side) is the one technically attaching the BB to the BB shell. The left (non-drive) side cup function is to press against the cartridge to prevent it from moving and support it against the BB shell.

If you needed to replace your BB, it would make sense to make the entire cartridge removable via the threads on the right side.

Hi e_guevara, yes, I think I agree; but eventually you'd want to be able to remove both sides in case of the need for replacement, i.e. to unscrew the right side with the BB and the left side cup. Thus it still doesn't appear to me plausible why only the BB (right) side had anti-seize paste, and not the left side cup. This is certainly not a "pressing issue", so I am just curious if anyone knows why Shimano applies anti-seize only to one side; i.e. why this makes sense to have anti-seize only on one side.

I never have seen a Shimano BB cup with anti seize factory applied. Lots of thread lock compound, lots of grease but never anti seize. Are you sure it was anti seize? The first thought I have is some one installed the BB and only felt they needed to use AS on that one side, for whatever their reasons were. Andy.

Shimano's cartridge BBs install with a spline tool get the one with a 3/8 square drive

and a breaker bar will be very insistant when you lean on the handle with enough force...

lefty tighty righty loosie in LH thread.

NDS is plastic It wont sieze , its not metal .. it mostly stabilizes the left end ..

Aluminum ones in a steel frame will do the same thing that sticks seatposts , then grease

or anti sieze in grease will be a good idea.. its the grease barrier layer mostly .. ..

Might be white lithium grease ? certainly Shimano wouldn't grease them before shipping

Hi Andrew and Fietsbob!
Good point to question whether the white paste that I reported is actually anti-seize. All I can confirm is that there was a very dry, rather "hard" paste on one of the threads of the originally shipped (new, unused) bottom bracket. I may very well be not an anti-seize but possibly a (lithium) grease. I may have jumped to conclusions when calling it anti-seize.

So, facts are: Bottom brackets were unused, brand-new BB55 with metal threads on both sides,
where the thread that is on the right drive side (which is solidly attached to the BB-body) was covered by "white stuff",
while the thread of the left side cup did not have such a coating.
Whatever the "white stuff" is, it was applied by the manufacturer.
Whether the "white stuff" was/is anti-seize or some kind of grease, I actually do not know.

The aluminum cup probably has an anodized treatment which is supposed to have built in anti-seize properties.
"Non-galling: Screws and other moving parts will not seize, drag or jam while wear in these areas is diminished. *** sights, instruments and screw threads are typical applications;"

If the white stuff is dry and slightly "rubbery" it is most likely a thread locking compound, which will also act as anti-seize. The NDS cup will need a light application of grease or anti-seize and the drive side can go in as is but clean the BB shell threads to remove residual grease first.

Didn't it come with instructions? Did read them?
Says to grease the fittings if metal to metal contact, especially if aluminum to steel.
That is not anti-seize on the threads, it's thread locker.

Hi Slash, SlowJoeCrow and Trialangel! Thanks for your responses.
(Trialangel, no, indeed it did not come with instructions, to my surprise.)
Yes, may well be that the single (left) side cap is anodized. It indeed made the impression that it is aluminum, while the thread of the bottom bracket (right side) appears to be steel. So, interestingly, since I have anodized my entire frame, and thus also the inside of my bottom bracket shell is now anodized, I probably would not even have needed any anti-seize (nor grease), right? (...because the anodization of the thread of my bottom bracket shell does that job already. But this is just a hypothetical question out of technical interest. To be safe, I will anyway apply grease as it is apparantly recommended by the manufacturer's instructions. [Thanks, trailangel to tell me.])

So, just to break it down to the working principles:
The recommendation to grease such threads, is that actually "just" a prevention for seizing?
I.e. "grease" is here just used/recommended as an anti-seize material, and not for any kind of "original purpose" of grease, i.e. lubrication?
That's how it appears to me.

From Wikipedia:
Seizing (or binding) can be caused by several factors:

1. Very close tolerances that prevent parts from moving.
2. Inter-metallic (galvanic) corrosion.

Grease solves (1) by lubrication. Grease solves (2) by insulating adjacent parts (as the job of lubrication), and by preventing ingress of H2O that causes oxidation (corrosion).

Hi e_guevara, yep, that's what I meant when I colloquially wrote "original purpose" of grease. The actual point was, it's only the anti-seize function that is needed in the bottom bracket thread, and not the lubrication bit of it. As, however, mostly one comes with the other, there is no point in differentiating in this occasion, I suppose.