Campagnolo Quick Release Seatpost Binder Bolt.
This is a handy item for sure - typically works wherever you would be able to fit a conventional Campy 8mm binder but you want flexibility instead. Also great for frames where the binder ears are messed up and the typical binder doesnt have a good area to bit into - this has big concial washer plates that grip the ears from the outside with lots of contact area. The binder is no lightweight - but it can be a real problem solver and a fun bit of Campy exotica on the cheap. We've sold these on ebay before at $40 - but this isn't ebay, its we hope a lot more fun!