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Bicycle Threading
#1
I just got off the phone with my brother, who can't understand all the reverse threading on a bike, and which ones are which. So I thought I would take a moment and explain which threads are what and why. Hopefully this can help some beginners out there.

Bottom Brackets
----------------

Bottom Brackets are threaded normally on the non-drive (left) and threaded reverse on the drive side (right).

So removal would be always turning towards the front wheel. Counter clockwise on the left, and clockwise on the right.

Pedals
------

Pedals are threaded normally on the drive side (right) and threaded reverse on the non-drive side (left). This is exactly opposite of the bottom bracket.

Removal would be always turning towards the rear wheel. Clockwise on the left, and counter-clockwise on the right.

A good memory mnemonic for pedals to BACK OFF. Turn towards the BACK of the bike to get the pedals OFF.



The reason for reverse threading is due to a process called Precession. A good explanation can be found here: http://en.wikipedia.org/wiki/Precession_%28mechanical%29
Dedicated scholar of bicycles
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#2
Bottom Brackets: not completely right. I own a bike that has two right threaded threads on the bottom bracket. It is a French bottom bracket (old Peugeot road bike). Not only is the direction different, but also the threading is metric rather than 'weird' inch stuff (like BSA). Also, the inner diameter is about half a mm wider than BSA, so a BSA cup will first look as if it fits and then come loose.
So when restoring an old road bike, sometimes you can get surprises when trying to remove the bottom bracket. I think there were also other types ob BBs that had two right threads...
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#3
You know, I actually had a disclaimer at the end of that post, saying "This is general information that will not apply to all parts, like obsolete French Bottom Brackets", but for some reason, I took it out.

Guess I should have left it in.Smile
Dedicated scholar of bicycles
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#4
*g well, I can be a nitpicker at times...
Well, the reason for me posting this was that my main problem when I started with bike stuff was that I had (still have) aforementioned clunker (I actually quite like it). So all information I found was not applicable. Well, I still learned quite a bit. (I have to admit my LBS did change the bottom bracket for me, I don't have the tools and there were other problems... I'm still thinking about rebuilding the original BB, I just have to get the correct bearings (deep grove bearings))
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#5
"Italian" bottom brackets are also threaded right handed on both sides but generally most bikes come with opposite handed threads. it's just you have to aware of the unusual ones.
Ride hard or ride home alone!
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#6
Extending existing threads is pretty straightforward if the shop is experienced, the threading die is sharp and they use plenty of cutting oil. The difficulty is in starting threads from scratch or threading a fork with a chromed steerer.
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