The RMS thread table is special in that it only includes a single thread size. This is due to the special history of this thread. The thread shown in the RMS thread table is an objective thread that is used in microscopy but also generally in the field of macro photography. The dimensions shown in the RMS thread table were proposed as a standard for microscope threads by the Royal Microscopical Society (RMS) in the middle of the 19th century. Up to this point, there was a confusion of different connection options for microscope objectives, which the RMS wanted to simplify. However, it was not until 1915 that the standard as it is reflected today in the RMS thread table was finally established.
The RMS thread is basically a simple Whitworth thread. As you can see from the RMS thread table, it is the W 0.8″ x 36 thread. Nevertheless, it is standardized independently as a microscope thread, for example according to DIN 58888, but also according to ASA B1.11, ISO 8038 or BS 7012-4.1. All these international standards refer to the same thread with the dimensions given in the RMS thread table.
As the thread is based on the Whitworth thread according to the RMS thread table, it also has a flank angle of 55°. It is also an imperial thread with a nominal diameter of 0.8″ and 36 threads per inch. In our RMS thread table, we have also compiled some important dimensions that you need to take into account if you want to work with the RMS thread. For the nut thread or internal thread, you can find information on the outer diameter and the core hole diameter in the RMS thread table. The bolt thread or external thread is also defined more precisely by these two values in the RMS thread table. As you can see from the RMS thread table, we have listed a minimum and a maximum value for each specification. The diameter actually achieved must be between these two values.