They are both the same size/shape. However, this doesn't necessarily mean the all Z ones will fit the R/X. Much depends on the design, size and shape of the plate(s) as to whether it will clear a centre stand, exhaust etc.

Some do happen to be a suitable profile for both R, X and Z models such as the Holan item (which is incidentally the cheapest one out there at just over �15+P&P).

http://holan.pl/en/xt660z-tenere/1524-side-stand-base-extension-yamaha-xt660-tenere.html#.VxP37zArLIU

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