Enter the knuckle radius R for a torispherical head as defined in ASME Section VIII Div. 1. For more information see Appendix 1-4 in the ASME code.
This dimension is usually referred to as IKR in many head catalogs. Even though the head catalogs list these heads as being OD
heads, the crown radius is given on the inside diameter basis. For example, DR and
IKR point to the inside of the head in the illustration.