Important information you need to know before beginning work on a motorcycle or ATV.


Use these links to find the information you need to know to properly repair your bike or quad. Don't guess at the meaning of terms in your repair manual. Get it right the first time.





Popular Abbreviations & Terms

These are common abbreviations used in our Repair Advice pages and in manufacturers' service manuals. Also refer to this page when the exact meaning of a word is in question.

Vehicle Identification Number

A Vehicle Identification Number or VIN is a unique identifying number given to all motor vehicles manufactured, sold or imported into the US. The majority of VINs are stamped into the frame of the bike, as well as on a VIN tag located on the frame.

Basic Repair & Diagnostic Tools

These are the basic tools you will need to begin repairs or maintenance of your bike or quad.

Advanced Repair & Diagnostic Tools

These are for more technically advanced and difficult repairs or hi-performance tuning.  Unless you are racing or building a custom bike you probably won't ever need to know about them.

Helmet Size Conversion Chart

Not all helmets are created equal.  Just because you wear a medium Shoei doesn't mean a medium Arai will fit.  Street helmet fitment often differs from offroad helmets from the same manufacturer.  This will give you a head start.  Never buy a helmet without trying it on!

Tire Size Conversion Chart and Speed Ratings

Looking for info on motorcycle, scooter, dirt bike or ATV tires?


SAE or Fraction to Metric Conversion

You should have paid more attention to your math teacher.  Can't remember if 4mm is bigger or smaller than 3/16?  We don't go insane here.  No one needs to know that 29/64 is 11.509mm while working on their kid's dirtbike.  We just give you the numbers you need.

Metric Bolt Sizes explained

OK the service manual says you need a 6x1.0x28mm bolt. Whaaaaaat?  What does thread pitch have to do with it?  You just need a bolt a little longer than an inch.  Why won't any one do? Before you jam just anything in there, check here.

Carburetor Jets

No matter how you spell it carberater, carberetor or carburetor, you still need to know what the carb

jets look like and what they do.


Electrical Symbols & Meanings

Read this page if you need help with how to read electrical symbols on motorcycle wiring diagrams and schematics, vintage and modern.
Electrical Symbols page

Spark Plug References

The primary function of the spark plug is to ignite the air/fuel mixture within the combustion chamber of the engine.

Our Spark Plug Cross Reference charts are based upon our preferred brand, NGK spark plugs. The NGK plug number is listed with the corresponding plug numbers from AC-Delco, Autolite, Bosch, Champion, Denso and Motorcraft. The plugs are listed in alpha-numeric order by NGK plug number.


Links to plug manufacturers' websites:




For information relating to a specific make and model {Honda CB750K, Suzuki GSX1100, etc}, such as sprocket and tire size, valve clearances and bike weight, please see the manufacturer's buttons in the navigation bar to the left or search this site for your bike.

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