Educate me about bolts please

[gmtfd]

Hi all

So I've noticed that bolts on old bikes are sometimes heavily corroded, while at other times they look brand new after a quick clean (e.g. those attached to high end Shimano stuff). I'm guessing that the former are made of steel with some sort of coating, which wears away over time. Might the latter type be stainless steel? I'm asking because I'm looking to get hold of new bolts for my current build. Also, I know the bolts found on bikes come in M3, M4, M5 etc, but is the thread pitch always the same for each type of bolt?

Cheers

Gareth

 

[marc two tone]

Yep, some bikes were thrown together. The aftermarket sector knew what they were doing with offerings of anodised and titanium bolt kits.
And yes, stainless bolts of m5 (bottle cage) and m6 (most other stuff) are cheap enough to justify a full bike's worth.

 

[captaincowelly]

Hi!
Some bolts were chromed steel (typically most 90's Shimano clamp bolts on shifters/levers/mechs etc.) and the plating can last indefinitely but often a bit of corrosion occurs,more so where the plating has been cracked due to over tightening.Bit of wire wool/autosol or similar can bring it up well.Looks a lot shinier than stainless.
Other bolts are anodised,often black.Not as hard wearing as chrome and more likely to corrode.Some are bright zinc plated (BZP) and have a gold/silver finish.Again,not as tough as chrome.
Not many stainless bolts used,probably a cost thing.Stainless bolts were often something upgraded by the owner.

 

[captaincowelly]

Oh,and the pitch is a pretty standard thing.If you order an M4/M5/M6 allen bolt it will be the right one for the bike.

 

[KermitGKona88]

Just be a bit careful as some components especially handlebar stems can bowl you a googly and have M7 bolts which were a swine to get replacements for.

 

[FluffyChicken]

Even worse when that M7 bolt needed a narrow head.
Filing Titanium bolt heads to make them narrow enough or chopping the end off to length, was hours of fun

A lot of things (mechs, brakes etc) you can look up what bolts they used, Shimano is very good at this and would often give you the length too.
Or just ask

Anyway, it's usually the chromed one that are top end, as mentioned.
You will fine bits of rust in the Allen hole often or where it scratch, often lifting it up or worming.

They're cheap enough to replace, harder to find in the exact style though.

 

[gmtfd]

Thanks for all the info chaps, very useful indeed. Now the question is, chrome plated steel, stainless steel or titanium? Titanium looks very pricey

 

[KermitGKona88]

Stainless is the best median cheap and cheerful, Ti is wonderful and light but very pricey and can gall or snap, chrome plated will eventually rust but this can be delayed by adding a covering of grease.

 

[hookooekoo]

is the thread pitch always the same for each type of bolt?

Metric threads can have a coarse or a fine pitch.

https://en.wikipedia.org/wiki/ISO_metric_screw_thread#Preferred_sizes
The small diameter threads on a bicycle will typically be coarse pitch (e.g. bottle cage bosses). Large diameter threads may be fine pitch (e.g. chainring bolts).

It's not worth worrying about, because you're unlikely to encounter problems unless you venture into areas such as wheel spindle threads. I had a little trouble a while back replacing a wheel spindle, and decided to buy metric and imperial thread pitch gauges. If you have pitch gauges and a digital vernier, you can identify any thread.

 

[captaincowelly]

Stainless is the best median cheap and cheerful, Ti is wonderful and light but very pricey and can gall or snap, chrome plated will eventually rust but this can be delayed by adding a covering of grease.

Have to agree with that.Stainless looks great,not expensive,loads of choice n will last forever.Ti great if you don't mind the extra ££'s for a few grammes of weight.Can be difficult finding chrome bolts in the right shape/sizes,probably gonna be more expensive than stainless.