R Style Oval Rings can be used only in Bottom Grooved Flanges.
R Style Oval & Octagonal Rings are interchangeable with Flat Bottom Grooved Flanges.
RX and R Style rings of Similar Nos are interchangeable .
BX and RX Style rings are not interchangeable standard API 6A and ASME B 16.20. We are looking for queries from India especially from North India & South India.