Rockcentrics are an excellent design, based on the old Chouinard Hexcentric, but much lighter and with a different, more curved, profile. However the principles of their use are the same.
The clever uneven sides mean that there are three sizes of placement each nut will fit, and they can also be cammed in horizontal breaks. Sizing is different from Hexes, with a size 7 being similar to a Hex 8.
Sizes 4 and 5 are smaller nuts, covering a similar range to the largest wires. Sizes 6, 7 and 8 are medium nuts and are all extremely useful in mountain areas such as Snowdonia and the Lake District. Size 9 is a good, light alternative to a big cam for granite cracks and gritsone edges.
Also available as a set 5-9.
(Sizes 1 and 2 have never been made and size 3 is no longer in production.)