Learn how to say Countersunk correctly in English with this tutorial pronunciation video.
Oxford dictionary definition of the word countersink:
Word forms: ˈcounterˌsunk, ˈcounterˌsinking
to enlarge the top part of (a hole in metal, wood, etc.) so that the head of a bolt, screw, etc. will fit flush with or below the surface
to sink the head of (a bolt, screw, etc.) into such a hole
a bit for countersinking holes
a countersunk hole