Countersink Hole Calculator Online (Flat-Head Screw Holes)

Countersink Hole Calculator (Flat-Head Screw Holes)

A countersunk screw must sit flush or slightly below the surface: an undersized csk hole leaves the head proud (scratching mating parts), an oversized one sinks it too deep. Wrong csk dimensions are a top rework cause in machining. This calculator outputs head diameter dk, head height k, clearance hole (GB/T 5277 close/medium/coarse), and the recommended csk diameter and depth.

Recommended practice: csk diameter = dk + 0.5 mm (centering margin for the 90-degree countersink tool), depth = k + 0.2 mm for flush assembly. Head dimensions follow GB/T 819.1 cross-recessed countersunk screws.

Machining tips: locate with a center drill before countersinking to avoid wandering; thin sheet may keep the head within 0.2 mm proud or use oval heads; deburr the hole mouth; add 0.1-0.2 mm depth in aluminum and plastics for spring-back; keep depth variation within 0.1 mm across a multi-hole panel. Pair with our bolt length calculator. Zhuhai Jiali Hardware supplies GB/T 819.1 countersunk screws in 304/316 stainless, zinc-plated and Dacromet - contact us.