8X38mm. These are the studs at the exhaust ports that the exhaust manifolds are bolted to. If they are in good shape then leave them alone, but if they are stripped, corroded, or broken off then you will need them. Each manifold is attached to the cylinder heads with 2 studs on one side and 2 bolts on the other side.
Ref ID: N144438
Ref ID: N144438