Remo Symmetry Conga drumheads are designed specifically for non-Remo model Congas equipped with the latest version 'contoured/radial' hoops, i.e rims, as a standard among conga manufacturers-beginning since the late 90's. (If you have traditional hoops or would prefer tucked conga drumheads, please see other knowledge base post to confirm if drumheads are available for your model or contact our support center). Symmetry drumheads are specifically engineered to conform to the shells bearing edge with tension for optimum tone, pitch stability, and projection. Denotation: 'D' in the model number, denotes the inner diameter (ID) of the Aluminum Ring. D1 being the smallest, D4 being the largest-all specific to the type/model of the drum. Note the Crown size, i.e.playing surface remains the same: 9.75", 10.75" 11.06", 11.25”, 11.75", 12.25” 12.50", 13”.Due to non-standardized conga drum manufacturing, drumhead fit may vary...make sure to center and level as you tension for optimum performance. All listed models have been fit tested by Remo staff. Gon Bop Congas: California Series, Alex Acuna Series Special Addition Series, Alex Acuna Signature Series, Tumbao Pro Series, Mariano Series. Drum sizes 10,11,11.25,12.25, 12.50"