RD “round tap” DIN 405

What are round threads?

Round threads (Rd) belong to the product group sliding threads. The threads can absorb very high forces. A round thread has a different profile shape in the nut than the spindle thread. The pitch of a round thread is given in inches. A typical designation would therefore be Rd 20×1/8.
This designation means a round thread with a nominal diameter of 20 mm and a pitch of 1/8 inch = 3.175 mm.
The drills are available in the sizes Rd 8 – Rd 36.

What does a round thread do? Where is a round thread used?

It is not a tap that cuts a thread, but cleans or forms it. These taps are used, for example, in nuclear power plants. There, all threads must be cleaned twice a year using a round tap. Round threads are also used, for example, as fastening threads in coupling and brake spindles of railway carriages and for large valves and slides. The round thread form makes this threaded spindle insensitive to dirt and damage.

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