That is a xtra 10 rear skid. it is a very nice riding and handling skid.
I had a 96 xcr600 that was the first year for the XCR to have the xtra 10. My other sled is a 00 xcsp600 and that has the xtra 10 in it as well. It is a much better skid than the proaction one.
I see this is for a TSS sled, I don't think that skid was even anywhere as good as the proaction skid, so this will be a huge upgrade.