Hi Shipto,
Just nipped out to check my el-cheapo set of weird driver bits. Nothing like your pic but if you imagine the reverse of that, i.e. where your mid section protrudes my bit has a cut out - (think two pronged fork) various sizes in this form. Don't ask what this type is called, not a clue.
Sorry mate, not a lot of help.
John B AKA Swarfnstuff