L – Blocks are defined by cracks that are non-spalled (sides of the crack are vertical) or lightly spalled, causing no FOD potential. Non-filled cracks have ¼ in. (6 mm) or less mean width and filled cracks have filler in satisfactory condition.

M - Blocks are defined by either: filled or non- filled cracks that are moderately spalled (some FOD potential); non-filled cracks that are not spalled or have only minor spalling (some FOD potential), but have a mean width greater than approximately ¼ in. (6 mm); or filled cracks greater than ¼ in. that are not spalled or have only minor spalling (some FOD potential), but have filler in unsatisfactory condition.

H - Blocks are well defined by cracks that are severely spalled, causing a definite FOD potential.