A square would be better to check each surface.
...IMHO > > > do the "BLADE" test for the CPU & the H50 Block surface.
....that being: to use a Blade of some sort(Stanley or whatever cutting blade) and a good flashlight(white light is better); and check the surface of both for of Gap's & Pit's or even for UNeven surface's of......
. . . just my 2 worth to mention of a "CHEAP" way to checkout BEFORE you apply TIM and hookup/connect . . . .