1 .Labelling: Bolts and Nuts have classifications and they are indicated by alphanumeric terms, such as:3A, 2B, 1A, etc. This indicates the thread class. The thread is the spiral engraving used in a bolt. From loose to tight the numbers increase. Example: 1 = loosest, 2 = medium and 3 = tightest. The letter A … Continue reading 7 Things You Should Know About Nuts & Bolts