Does anyone know what this nut/bolt is and what tool would fit it? - I can probably make do with some adjustable spanners but I'd rather get the right tool.

It's for a 10 year old bike (A Scott Purgatory mountain bike) - I think I asked the guy at the shop to take off the quick releases to stop my wheels getting stolen, but have long since lost the tools that fit this.

Any help much appreciated!