This is a naming convention adopted by the American National Standards Institute (ANSI). For HPLC fittings, the first number indicates the diameter of the threaded portion of the nut (not the tubing that goes inside). When the diameter is less than ¼”, as it is in this case, a gauge value is used (gauge 10). The number following the hyphen refers to the number of threads per inch, thus indicating the “pitch” of the threads. An external screw thread size and tolerances chart is available here: http://www.engineersedge.com/screw_threads_chart.htm
10-gauge fittings are approximately 3/16″ in diameter.
Size 10-32 fittings have a thread count of 32 threads per inch. Note that the first thread is used to align the fitting at zero and is not included in the thread count.
