Bolt types and sizes

For discussions about bikes and equipment.
skyhawk
Posts: 280
Joined: 30 May 2019, 3:00pm

Bolt types and sizes

Postby skyhawk » 14 Jun 2019, 11:55am

Are bolts on bikes mostly a standard size.

I need to replace a few as I have not ridden for some time (UK)

See attached images.

They look to be 8mm by the length

Thanks

Dscn0411.jpg


Dscn0410.jpg
Both I and my son are Autistic. We have aspergers and ADHD, not stupid :). If I sound "blunt" in my posts, please be understanding : I am not perfect. Thank you. Visit https://www.asdinfowales.co.uk/ to learn more

pwa
Posts: 9859
Joined: 2 Oct 2011, 8:55pm

Re: Bolt types and sizes

Postby pwa » 14 Jun 2019, 12:08pm

SJS Cycles are a pretty good source of bolts for bikes.


https://www.sjscycles.co.uk/nuts-bolts/

https://www.sjscycles.co.uk/chainsets/t ... pack-of-5/

Given the relatively low cost of hex head bolts it is my policy to keep a few of each commonly required size in the back of the garage, all stainless.

What did the bolt in the top pic come off?

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Cugel
Posts: 2195
Joined: 13 Nov 2017, 11:14am

Re: Bolt types and sizes

Postby Cugel » 14 Jun 2019, 12:43pm

skyhawk wrote:Are bolts on bikes mostly a standard size.

I need to replace a few as I have not ridden for some time (UK)

See attached images.

They look to be 8mm by the length

Thanks

Dscn0411.jpg

Dscn0410.jpg


These tools are very useful for determining the size and thread-pitch of bolts:

https://www.amazon.co.uk/Deals%E3%80%91 ... pons&psc=1

https://www.amazon.co.uk/Silverline-675 ... ay&sr=8-13

Manual-read verniers are better than the electronic ones as the latter can too easily go defunct i' the electronics.

In addition, it can help to find the right configuration of bolt by knowing which bike-part the original came from. Some bolts have very specific lengths and head-shapes that may need to be exact if they're to fit.

Another thing to watch out for is the type of driver needed to tighten or loosen the bolt. Allen key heads are generally all metric (but there are some that might be imperial). Many Japanese bolt heads take a JIS screwdriver tip rather than a Philips. They're not the same shape even though they look similar to the naked eye. A Philips screwdriver can cam-out of a JIS head and damage it, especially on the teeny bolts found in derailleur throw adjustment screws and similar.

Cugel

alexnharvey
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Joined: 10 Jan 2014, 8:39am

Re: Bolt types and sizes

Postby alexnharvey » 14 Jun 2019, 12:56pm

Modern bicycle bolts are mostly metric. They may however have non standard heads, use non standard hex keys for their diameter and have fine rather than regular threads. Bolts also vary in material and strength, so you can buy low and high tensile strength bolts and also plain steel, plated, treated or stainless steel.

Your first bolt looks like it has fine threads for the diameter and a very shallow head, a bit like a chainring bolt. On the other hand the second looks to be a relatively standard metric bolt in Chrome plated steel. Can't tell if it's M6 or M8.

When you say they 8mm long, what have you measured? The main measurement is the diameter of the shaft rather than the head. So an M8 bolt has a 8mm diameter threaded portion.

See here for standard sizes https://www.engineersedge.com/hardware/ ... _14054.htm

If you say what those bolts were doing on the bike it is very likely someone here can help you find replacements.

If I need a bolt I normally buy 5 or 10 of them from a bolt supplier on eBay, normally in stainless steel too, for a couple of pounds. There are a few exceptions that are very specific to bikes that must be purchased from a bike shop or specialist.

Brucey
Posts: 34821
Joined: 4 Jan 2012, 6:25pm

Re: Bolt types and sizes

Postby Brucey » 14 Jun 2019, 4:51pm

the two bolts you picture are non-standard bolts. Its impossible to say for sure what they are from the photos but my best guess is


a) a chainring bolt, M8 x 0,75 threaded. If so, this thread and head shape is pretty much only found on bicycles. That particular bolt looks like it maybe came from an old stronglight chainset.


b) a M8 x 1.25mm (or M7 x 1mm) threaded bolt with a non-standard head. If M8 the thread size is a very standard but the head size is not; specifically the usual M8 x 1.25mm caphead has a head that is wider than the bolt shown. You may be able to modify a standard caphead by machining the head down. If M7x1, again this thread size and bolt form is highly bicycle specific; this kind of bolt is found on stems.

In many cases it is easiest to live with the rubbish finish on the bolts you have (eg clean them up and paint them) rather than source new ones.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

skyhawk
Posts: 280
Joined: 30 May 2019, 3:00pm

Re: Bolt types and sizes

Postby skyhawk » 14 Jun 2019, 7:58pm

Thanks, I think it is right they are M8
Both I and my son are Autistic. We have aspergers and ADHD, not stupid :). If I sound "blunt" in my posts, please be understanding : I am not perfect. Thank you. Visit https://www.asdinfowales.co.uk/ to learn more

PT1029
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Joined: 16 Apr 2012, 9:20pm

Re: Bolt types and sizes

Postby PT1029 » 14 Jun 2019, 8:53pm

My hunch is the top bolt is for bolting an inner chain ring to an older Shimano triple crank - the tread length (to me) suggests the older design where there is a separate spacer between the inner chain ring and the crank.
On later models the crank forging had more protruding mounting points for the inner ring, so the separate spacer is no longer needed (as it is effectively now part of the crank) - this design means a shorter bolt can be used. If you need a replacement bolt as per the picture, probably hard to come by (use the wanted pages on here?).

The lower bolt, my hunch is a bolt for clamping the handle bars in a handle bar stem (though various sizes exist, depending on made/model). If you need to replace a missing bolt, scavenging from an old stem might be the easiest way.

A bolt supplier might have some of these, ie, the same threaded section, but the heads would probably need grinding down or some such.

As Brucey says, the bolts in the pictures are perfectly OK to use.

skyhawk
Posts: 280
Joined: 30 May 2019, 3:00pm

Re: Bolt types and sizes

Postby skyhawk » 15 Jun 2019, 11:53am

MY fault, sorry, I will in future be more explicit when posting questions.

The bolts come from here (the large ones anyway)

And BOY are you right, the other IS from the handlebars

Dscn0416.jpg
Both I and my son are Autistic. We have aspergers and ADHD, not stupid :). If I sound "blunt" in my posts, please be understanding : I am not perfect. Thank you. Visit https://www.asdinfowales.co.uk/ to learn more

Carlton green
Posts: 124
Joined: 22 Jun 2019, 12:27pm

Re: Bolt types and sizes

Postby Carlton green » 22 Jun 2019, 2:01pm

“Are bolts on bikes mostly a standard size.

I need to replace a few as I have not ridden for some time (UK)”

Screw thread sizes used on bikes are all to standards, but not necessarily standards that are in common use elsewhere. To add to the confusion some threads are also left rather than right handed. IIRC one of the bottom bracket cups has a left handed thread and so does one of the pedals.

Metric is predominantly used on bikes bikes now but in the past they were various forms of Imperial including British standard cycle.

You have no doubt solved your initial problem by now but in general it’s best to clean up the fastening (screw) that you have and refit it rather than try to replace with new - what you have is guaranteed to fit and what (replacement) you get might fit or might damage the mating part.

Hope that’s a help to someone.

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Mick F
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Re: Bolt types and sizes

Postby Mick F » 22 Jun 2019, 2:19pm

Good advice there! :D

When I've wanted to change a bolt or screw for a new one - usually from rusty chrome to stainless - I've taken the part to our nut 'n' bolts place in Plymouth to see if they can check if it's one they have in stock.

http://www.expressfixing.co.uk
It's a delight to see what they have in there. Excellent service, and very knowledgable indeed.
Mick F. Cornwall

skyhawk
Posts: 280
Joined: 30 May 2019, 3:00pm

Re: Bolt types and sizes

Postby skyhawk » 22 Jun 2019, 3:17pm

Mick F wrote:Good advice there! :D

When I've wanted to change a bolt or screw for a new one - usually from rusty chrome to stainless - I've taken the part to our nut 'n' bolts place in Plymouth to see if they can check if it's one they have in stock.

http://www.expressfixing.co.uk
It's a delight to see what they have in there. Excellent service, and very knowledgable indeed.



:(

Shame I used to live in Tavistock, now wales
Both I and my son are Autistic. We have aspergers and ADHD, not stupid :). If I sound "blunt" in my posts, please be understanding : I am not perfect. Thank you. Visit https://www.asdinfowales.co.uk/ to learn more