24mm shallow socket ( about £6 on eBay )Data wrote:As said the exhaust does not have to come off. But the filter is still a little awkward to get at so get a filter removal tool. Chain or strap type is best. Again Halfords do a nice chain type for £4.95 that will fit the small size of the GTS.I did mine without the tool but wished I had used one as it's quicker and easier.
There’s also a special tool for the slotted filter .