Mucky Nutz R/CX Butt Fender It prevents 'soggy arse syndrome' i.e. your derriere getting soaked from the mud and rainwater thrown from your back wheel It is fitted as close as possible to said back face for optimum 'muck' catching No need for separate fasteners, so it's easy to fit and take off it's possibly the lightest rear mudguard available, at just 15g It's compatible with all standard double rail saddles, so long as they don't have any daft bits hanging off the rear