Is it Glenn who you've been put onto? He made some at work out of nylon for his bike and i reckon a guy called Jason Dawes (who recently defected to Aprilia...) also used some.

They mount on the long bolt that goes through the engine at the front and the two hangers that drop down from the main frame spas. Might be ok if you have a tame low side but if the bike landed on one of the sliders from a highside or hit a curb as it slid along the ground, the impact would bend the frame hangers and push the engine to one side, knackering the frame. As the dude above points out.

There aren't any really strong places to put any sliders on the frame.

When i highsided my '21 at Cadwell park, it landed on the right handlebar, snapping it and the throttle assembly in half and pushed the forks out of line. If it'd landed on a frame slider mounted off the front engine hanger, the force would've bent something much more important than any paintwork it might've saved.
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After years of moaning about immigrants now i am one...