2022-06-25 - Bike Bolt Sizing
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Yesterday as i was riding my bike, two bolts fell out and my rear
rack swung loose.  Fortunately, i had two spare rack bolts screwed
into my front fork.  Now it is time for me to replace those spares,
and i need to figure out what size they are.  The manual does not
include the bolt sizes in the specifications.  Below is some helpful
information that i found at bicyclebolts.com

By the way, i would not buy these bolts online.  They are inexpensive
and do not cost any shipping at BiMart or the local hardware store.

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When measuring a bolt, it's best to use calipers and a thread
checker.  You can probably work it out with a metric ruler though.

For example, take this M5-0.8 x 16mm:

How to size your bolts
<gopher://tilde.pink/I/~bencollver/log/2022-06-25-bike-bolt-sizing/
Bolt_sizing_doc.jpg>

The bolt size is M5.  You determine this by measuring the diameter of
the shaft in mm to come up with the "M5" value.  The socket wrench
the bolt uses does not determine the bolt size.  This is a common
mistake.

The bolt length is measured from the end of the threads to the bottom
of the bolt head.  That's the length of the shaft, excluding the
head.  In the example it is 16mm long.

The thread pitch is the distance between threads measured in
millimeters along the length of the bolt.  Determining the thread
pitch can be difficult without a thread checker tool.  The bolts on
this sight use the standard thread pitch per size.  I'm sure there
are some odd balls out there but generally speaking, bicycles and
bicycle parts use bolts with these thread pitches.

* M5 = 0.8 thread pitch
* M6 = 1.0 thread pitch
* M7 = 1.0 thread pitch
* M8 = 1.25 thread pitch

There is a lot variability in what size bolts manufacturers use use
for their parts.  Here is a general guide fo the most common bolt
sizes.  

Common bike bolt sizes
<gopher://tilde.pink/I/~bencollver/log/2022-06-25-bike-bolt-sizing/
common_bolt_sizes.jpg>

One common mistake is thinking the size wrench you use correlates to
the size of your bolt.  For example the bolt used to attach your
bottle cage is not an M4 because you use an M4 wrench.  Bottle cages
always use M5 bolts.

tags: bencollver,bicycle,repair

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