THREAD INSPECTION OR MEASUREMENT?

By ”inspection” means checking threads with solid gauges and preferably with both Go and No-Go thread plug and ring gauges. This applies in most cases, to smaller diameter standard threads cut with taps or dies. Gauges for smaller standard threads are usually reasonably priced although, if gauges are for non standard threads or to be calibrated regularly, cost increases.

Measuring threads is common sense especially when setting up the machine. Making a mistake in expensive items is costly and certainly cause for concern if it is a customer that finds a fault. When measuring always measure d or D1 and preferably pitch diameter. If the pitch diameter is close to the middle of the tolerance then inspection probably doesn’t need to be as often and with mass production SPC will show how much variation there in fact is within the tolerance by the process. There will almost certainly be much less wear on solid gauges by staying away from tolerance limits.

The major diameter (d) of an external thread must not be less than the minimum of the tolerance and the minor (bore) diameter (D1) of an internal thread must not be more than the maximum of the tolerance. Both these measurements are very easy to do and a stripped (weakened) thread could be a disaster.