M20 thread: tap drill, clearance hole and counterbore sizes
The hole sizes and depths for an M20 coarse thread, and how to put it on a drawing.
| Property | Value |
|---|---|
| Nominal diameter | 20 mm |
| Pitch (coarse) | 2.5 mm |
| Tap drill | Ø17.5 mm |
| Clearance hole, fine | Ø21 mm |
| Clearance hole, medium | Ø22 mm |
| Clearance hole, coarse | Ø24 mm |
| Socket head cap screw head Ø (ISO 4762) | 30 mm |
| Counterbore Ø (DIN 974-1) | 33 mm |
| Counterbore depth (head flush) | about 20.5 mm |
Thread depth
| Material | Full thread engagement |
|---|---|
| Steel, stainless steel | 20–30 mm |
| Aluminium, brass | 30–40 mm |
| Plastics | 40–50 mm or an insert |
Drill the tap hole at least 7.5–10 mm (3–4 pitches) deeper than the full thread, plus the drill point. More on this in how deep a tapped thread should be.
How to call it out on a drawing
Tapped blind hole: M20x2.5-6H, thread 30 deep, tap drill Ø17.5 40 deep.
Clearance hole with counterbore: Ø22 through, counterbore Ø33 × 20.5 deep.
M16 | M24 | All thread sizes
Draw your own part
Drop a STEP file into DrawMyPart. It finds every body, asks you to confirm threads, fits and tolerances, and draws a sheet your manufacturer can build from.
Open the tool