Bolts are the main fastening components of nearly all modern machines, and should always be accounted for when servicing your car. Specific bolts are used throughout your vehicle, and special care to replace them should be observed when doing important service, especially on engine components. Light gray aluminum torque-to-yield bolts (any bolt which has a torque spec that includes an additional angle when tightening) must be replaced every time to avoid snapping, as they are designed to be one time use. Important dimensions to keep in mind when looking for the right bolt are the bolt head (usually in millimeters, the size of your wrench), the bolt size (in metric, this would be something like M8, meaning 8mm diameter), and thread pitch (also generally referenced in mm). Using the wrong bolt for a specific job is a risky endeavour and can lead to problems in the future.