Toyota Prius 2010 Repair Manual page 182

Measurement point:
115 mm (4.53 in.)
Standard diameter:
9.77 to 9.96 mm (0.385 to 0.392 in.)
Minimum diameter:
9.4 mm (0.370 in.)
If the diameter is less than the minimum, replace the cylinder head bolt.
HINT:
If a visual check reveals no excessively thin areas, check the center of the bolt (refer to illustration) and find the
area that has the smallest diameter.
18. INSPECT EXHAUST MANIFOLD
2010 Toyota Prius
(a) Using a precision straightedge and feeler gauge, measure the warpage
on the surface that contacts the cylinder head.
Maximum warpage:
0.7 mm (0.0276 in.)
If the warpage is more than the maximum, replace the exhaust manifold.
Repair Manual