London, assuming you are talking about an XT660X / XT660R and not the Tenere XT660Z this is the DNA Stage 2 filter for the X/R

It replaces the side cover (right leg side) with a new filter opening which gives the bike the max oomph possible.

http://www.e-dnafilters.com/Product.asp?ID=665

similar to the Tenere's Stage 2 filter cover as in the link below:

http://www.e-dnafilters.com/Product.asp?ID=1211