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Discussion Starter #1
Please forgive my ignorance but the more I try to search for an answer, the more frustrated I become... That's what this community is for I suppose.

I need help identifying the M ratings for the following bolts on the front end of my 2006 749s:
-Caplier bolts M8 x 15 (I THINK this is right)
- rotor bolts ? (no idea)
- Pinch bolts M8 x 20 (again, I THINK)

I thank you all in advance for trying to help me with these bolts, mine are oxidizing and need to be replaced.
 

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Discussion Starter #4
M is the diameter of the screw, M8=8mm. The x 15 or x 20 is the length, under the head of the screw. Except for flathead screws, which are measured the overall length.

Here is a pretty good information page.

http://www.aaronsmetricscrews.com/
Does the M rating for the width include thread to thread or is it the width INSIDE of the threading?

Is there any way to get the info on specific ducati bikes?
 

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Outside diameter of the threaded portion. There will be another specification, for an example, M8 x 20, 1.25 pitch, that is the space between each thread, point to point, here is a really lowtech example down on the left, the measurement would be the 2 horizontal lines I typed there.

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Does the M rating for the width include thread to thread or is it the width INSIDE of the threading?

Is there any way to get the info on specific ducati bikes?
if I understand the question, m is not any kind of rating it is metric size and is nominal ex an 8mm bolt will not fit into a 8mm hole there must be some clearance and that takes you to the thread class
the rating as you call it will be marked with a 5.9 9.8 or some such thing or with markings similar to sae bolts, if it is not marked then you must do the math for the application specs.
please dont be tempted to just buy hardware stoe bolts because they fit, if you need help in person my first stop would be fastenal, they are expensive by the pc but its their bis.
 

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Discussion Starter #7
if I understand the question, m is not any kind of rating it is metric size and is nominal ex an 8mm bolt will not fit into a 8mm hole there must be some clearance and that takes you to the thread class
the rating as you call it will be marked with a 5.9 9.8 or some such thing or with markings similar to sae bolts, if it is not marked then you must do the math for the application specs.
please dont be tempted to just buy hardware stoe bolts because they fit, if you need help in person my first stop would be fastenal, they are expensive by the pc but its their bis.
Thanks for your concern. I will be splurging on Ti bolts from racebolts.com. Now I am concerned about the space between the threading. This website has so many options and all I have is a ruler.

Also thanks for all this constructive feedback! I've learned so much in such a short period of time! Cheers
 

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threadspacing...think he means pitch...see corndog67 post above
Pitch is the distance from the crest of one thread to the next...
SAE usually expresses threads per inch
Metric expresses distance from the crest of one thread to the next
 

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You can buy a thread pitch gage for probably less than $10. Check with Enco tools or maybe MSC Tools. They sell metric and inch sizes.

Google metric screws and check some of those sites for the different ratings that are usually shown on the top of cap screws, i.e.: 8.8, 12.8. Those are differing grades of strength of the screw, the higher the number the higher the rating (strength). The same system is used for inch screws also, referred to as grade 5, grade 8 and higher. I stick with grade 8 and up for motorcycles. Most of the socket head cap screws they sell at Orchard Supply and Hardware, our local store, are grade 8 and up. You can pay $1.09 for 2 M6 x 20, 1.0 pitch, but a box of 100 can be had for about $8.50 from McMaster Carr. I'd rather get the good deal, just on principle, and have 98 extra screws.
 
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