فارسیIdentifying the thread of a bolt or screw is quite easy. To identify a bolt or screw you need to know
the diameter of the bolt
the number of threads per inch (or pitch) on the bolt
These results are compared to information on a thread chart to identify the thread type.
Measuring the diameter of a bolt or screw
This is best done with a micrometer or vernier. If you do not have access to this equipment careful measurement using a steel rule will be fine for sizes 1/4” and up.
Measuring the threads per inch (or pitch)
Metric threads are measured by their pitch. That is the distance from the crest of one thread to the crest of the next measured in millimetres. The pitch of a metric thread can be checked by direct measurement with a
metric rule.
Imperial threads have their pitch measured indirectly as a given number of teeth per inch.
Use a steel rule to find the pitch or teeth per inch of a thread
Place a rule along the thread, parallel to its axis.
Line up the crest of one tooth with a major division
Count the number of teeth to match a whole number of divisions
Calculate the number of threads per inch
A much easier and more accurate way to identify the pitch of a bolt is to use a thread gauge (also known as a screw pitch gauge). These gauges consist of a steel case with a number of folding leaves at each end. Each leaf has teeth of a particular pitch, which is marked on the leaf. Using the bolt pitch and diameter compare this to the information on thread charts to try to identify the thread type.
