Cycling and bicycle discussion forums. 
   Click here to join our community Log in to access your Control Panel  


Go Back   > >

Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

User Tag List

Reply
 
Thread Tools Search this Thread
Old 12-11-05, 11:23 AM   #1
trigeak13
Newbie
Thread Starter
 
Join Date: Dec 2005
Bikes:
Posts: 4
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Can some explane bolts for me (m5, m6, m8... what's the difference)?

I understand threads per inch, standard bolt sizes, but what the hell does this M# mean?
trigeak13 is offline   Reply With Quote
Old 12-11-05, 11:33 AM   #2
royalflash
Senior Member
 
royalflash's Avatar
 
Join Date: Mar 2004
Location: Munich
Bikes: Lemond Alpe d´Huez, Scott Sub 10, homemade mtb, Radlbauer adler (old city bike), Dahon impulse (folder with 20 inch wheels), haibike eq xduro
Posts: 1,372
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by trigeak13
I understand threads per inch, standard bolt sizes, but what the hell does this M# mean?

M=metric and the following number is the thread diameter in mm. Thus M5 has a 5mm diameter thread (not the diameter of spanner you need). An M5 needs an 8 mm spanner.
__________________
only the dead have seen the end of mass motorized stupidity

Plato

(well if he was alive today he would have written it)
royalflash is offline   Reply With Quote
Old 12-11-05, 11:39 AM   #3
Sheldon Brown
Gone, but not forgotten
 
Sheldon Brown's Avatar
 
Join Date: Jul 2002
Location: Newtonville, Massachusetts
Bikes: See: http://sheldonbrown.org/bicycles
Posts: 2,301
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by trigeak13
I understand threads per inch, standard bolt sizes, but what the hell does this M# mean?
The "M" means "metric."

Metric threads are designated by diameter and thread spacing. For instance, the most common bolt size used on bicycles is 5 x .8, also known as "M5." This size is used for water bottle mounts, cable anchor bolts, fender/rack eyelets, shifter mounts etc.

The "5" means the bolt diameter is 5 mm. The ".8" means that the threads are .8 mm apart.

5 mm diameter hardware with different thread pitches also exists, and is occasionally seen on older French stuff and the like. The "M" designation is shorthand to indicate the standard coarse thread pitch (.8 mm in the case of "M5")

M6 is 6 x 1 mm threading. This is the second most common threading on bikes, used for brake mounting bolts, threadless stems and other things.

M8 is, I believe 8 x 1.25 mm threading though, again, there are other pitches used in the 8 mm diameter.

As another example, chainring stack bolts are commonly 10 x 1 mm, which is a fine thread, so they would not be called "M10", since "M10" refers to the 10 x 1.5 mm size, not commonly used on bicycles.

Sheldon "Numbers" Brown
Code:
+-------------------------------------------+
|   Originality is undetected plagiarism.   |
|                        --Dean W.R. Inge   |
+-------------------------------------------+
Sheldon Brown is offline   Reply With Quote
Old 12-11-05, 12:33 PM   #4
MudPie
Senior Member
 
MudPie's Avatar
 
Join Date: May 2004
Location: Southern California
Bikes:
Posts: 1,874
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by royalflash
...Thus M5 has a 5mm diameter thread (not the diameter of spanner you need). An M5 needs an 8 mm spanner.
I'm glad you mentioned the fastener size is not the same as the spanner size, a fairly common error.

For the Americans, "spanner" = "wrench".
MudPie is offline   Reply With Quote
Old 12-11-05, 01:23 PM   #5
HillRider 
Senior Member
 
Join Date: Aug 2005
Location: Pittsburgh, PA
Bikes: '''96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '12 Surly Pacer, All are 3x8,9 or 10. It is hilly around here!
Posts: 28,852
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 66 Post(s)
Sheldon is correct that there are different thread pitches for a given bolt diameter in metric sizes just as there are two "standard" series of English bolts, NC and NF threads. For example the most common 1/4" bolt is 1/4-20 (an NC size) or 1/4" diameter by 20 threads per inch but there is also a 1/4-28 in the NF series.

As noted, the "standard" 8 mm bolt is 8 mmx1.25 mm but the crank bolts on square taper bottom brackets are 8 mm x 1.0 mm.
HillRider is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -6. The time now is 03:25 PM.