Tech Brief | A Field Guide to 14 Standard Holes in Mechanical Design
Besides of welding, our workers drill holes every day, yet fewer than 10 % truly master the 14 standard hole types. Here is the complete cheat sheet.
Why Hole Selection Matters
Why Holse Selection Matters- Assembly, fluid passage, weight reduction, sealing—eachfunction demands a different hole.
- Wrong selection causes misalignment, stress concentration,leakage or assembly failure.
- CAD call-outs, CNC tooling and inspection must match the designintent.
14 Global Hole Types at a Glance
# | Hole Type | Typical Section | Primary Function | Common Symbol |
1 | Simple hole | Straight circular | Clearance or pilot | Ø |
2 | Through hole | Full-depth | Wiring, flow, fastener | Ø … THRU |
3 | Blind hole | One-sided | Thread base, weight relief | Ø … ↓ … |
4 | Interrupted hole | Discontinuous | Bearing seat, dowel | Segment notation |
5 | Tapped / threaded hole | Internal thread | Screw retention | M×P×D |
6 | Taper hole | Conical | Seal, press fit | Taper or angle |
7 | Counterbore (spot-face) | Cylindrical recess | Hex bolt/O-ring seat | ⌴ |
8 | Countersink | Conical recess | Flat-head screw | ⌵ |
9 | Counter drill | Conical recess | Rivet / screw flush | ⌵+angle |
10 | Counterbore-flat bottom | Flat recess | Uniform load | ⌴+SF |
11 | Clearance hole | Oversized | Free bolt passage | Ø≥(d+Δ) |
12 | Reamed hole | Precision bore | High accuracy/finish | H7, H8 |
13 | Overlapping hole | Intersecting circles | Special assemblies | Overlap call-out |
14 | Micro-hole (EDM/Laser) | Sub-mm | Jet, sensor | Laser/EDM note |
Five-Step Selection Checklist
- Function – fasten, flow, seal?
- Dimension – diameter, depth, tolerance, Ra.
- Material – steel, plastic, composite → tool match.
- Process – CNC drill/mill/tap, EDM, laser?
- Standard – ISO 273 (clearance), ISO 4762 (countersink), ASMEY14.5 (GD&T).
Machining Parameters Quick Pick
Material | Tool Type | Cutting Speed (m/min) | Feed (mm/rev) |
Carbon steel | HSS or carbide | 20–40 | 0.1–0.3 |
Stainless steel | Cobalt drill | 15–25 | 0.08–0.2 |
Aluminum alloy | HSS | 60–120 | 0.2–0.4 |
Plastics | Plastic-specific drill | 80–200 | 0.1–0.3 |
Typical Call-Out Examples
- M6×1.0-6H ↓ 10 → Threaded hole M6, pitch 1.0, depth 10 mm
- Ø10 H7 THRU → Through hole Ø10, tolerance H7
- ⌴Ø20×10 → Counterbore Ø20, depth10 mm
