What is a screw thread call-out for English fittings?
This is a common system for describing the threading on a fitting or screw cap that uses the English method.
The thread Call-Out normally consists of two numbers where the first number will refer to the diameter of the widest thread and the second one refers to how many threads per inch the fitting has (aka thread pitch). In other terms, this refers to how close the threads are to each other.
One needs to match the thread “Call-Out” of the fitting or cap to the receiving port it is going into. In other words, you need a 1/4-28 male fitting for a 1/4-28 female fitting.
It should be noted that when fittings designed in “English” system (non-metric) are smaller than 1/4″, the diameter of the thread is not given in inches; it is given in “gauge”. An example of this would be a 10-32 thread. This refers to 10 gauge and 32 threads per Inch.