Aka Sliders. Not really camming devices, more spring loaded wedges.
Good for very thin cracks.
In a totally unscientific test conducted in a local quarry, one member of our staff pronounced himself very impressed - "incredibly strong and stable placements even in the smallest size"
A better idea of the usefulness of Ball Nuts can be gained from viewing the short video below. A size 1 Ballnut was the only protection on the lower/hard section of The Promise at Burbage South. Initially the route was graded E10, 7a but once climbers realised how good the Ballnut placement was - the grade came down to E7 7a. That is how good they are! Unfortunately the placement has deteriorated with use and it is now done with loads of pads and is up to E8 (and presumably E10 without the pads).
Currently not available in the UK - we hope to get stock sometime in 2024.....