Before we can start to work with fasteners we need to be able to use some accurate measuring tools.  

How can I figure out what size bolt/nut to buy?

Step #1 Identify whether your bolt is (Metric or Standard)

Step #2 Measure the major thread diameter of your bolt

Step #3 Identify your thread pitch if your fastener is metric or your thread count if your fastener is standard

Step #4 Measure the length of your fastener

Step #5 Identify the grade of your fastener