Frontpipe to manifold and MIddle section to catalyst nut.
This is M12 x 1.25mm with a 17mm Hex which is quite rare.
This size hex allows you to use a normal socket on the front pipe to manifold studs
making fitting the frontpipe a whole lot easier

V6 FTO's use 4 of these on the frontpipe to exhaust manifold & 2 of these on catalyst to middle section of the exhaust.
1.8 FTO's use 2 of these on the frontpipe to exhaust manifold & 2 of these on catalyst to middle section of the exhaust.
For Exploded Diagram of these locations See HERE

Mitsubishi Part Number
MB059359