Metric thread pitch, tap drill and clearance hole sizes, gauge to millimetre conversion, and how screw length is actually measured. Everything you need to specify a screw correctly on a drawing or a purchase order.
Request a Quote → WhatsApp UsThe ISO metric coarse series is the default for general assembly. The tap drill column gives the hole to drill before cutting an internal thread; the clearance column gives the through-hole for the screw to pass freely.
| Size | Coarse pitch (mm) | Fine pitch (mm) | Tap drill (mm) | Clearance hole (mm) |
|---|---|---|---|---|
| M1.6 | 0.35 | n/a | 1.25 | 1.8 |
| M2 | 0.40 | n/a | 1.60 | 2.4 |
| M2.5 | 0.45 | n/a | 2.05 | 2.9 |
| M3 | 0.50 | 0.35 | 2.50 | 3.4 |
| M4 | 0.70 | 0.50 | 3.30 | 4.5 |
| M5 | 0.80 | 0.50 | 4.20 | 5.5 |
| M6 | 1.00 | 0.75 | 5.00 | 6.6 |
| M8 | 1.25 | 1.00 | 6.80 | 9.0 |
| M10 | 1.50 | 1.25 | 8.50 | 11.0 |
| M12 | 1.75 | 1.25 / 1.50 | 10.20 | 13.5 |
| M14 | 2.00 | 1.50 | 12.00 | 15.5 |
| M16 | 2.00 | 1.50 | 14.00 | 17.5 |
Pitches per ISO 261. Clearance holes per ISO 273 medium fit. Tap drills are the standard 100 percent minus allowance sizes used for coarse threads.
We manufacture machine screws across the full M2 to M16 range in both coarse and fine pitch, to DIN and ISO dimensional standards.
Wood screws and self tapping screws are traditionally specified by a gauge number rather than a metric diameter. Gauge refers to the major diameter of the thread, not the shank or the head.
| Gauge | Nominal Ø (mm) | Nominal Ø (inch) | Common applications |
|---|---|---|---|
| #2 | 2.2 | 0.086 | Fine electronics, small hardware |
| #4 | 2.9 | 0.112 | Thin sheet, electronics, light trim |
| #6 | 3.5 | 0.138 | Light enclosures, cabinet hardware |
| #7 | 3.9 | 0.151 | General sheet metal and joinery |
| #8 | 4.2 | 0.164 | Ducting, brackets, general fixing |
| #10 | 4.8 | 0.190 | Heavier gauge sheet, structural fixings |
| #12 | 5.5 | 0.216 | Light structural fabrication |
| #14 | 6.3 | 0.242 | Thick sheet, heavy brackets |
These sizes cover our self tapping screws (2.9 to 6.3 mm), wood screws (3 to 8 mm) and chipboard screws (3 to 6 mm).
This is the single most common specification error we see on incoming drawings. The rule depends on whether the head sits in the material or on it.
| Head style | Measured from | Why |
|---|---|---|
| Countersunk (CSK), Raised CSK, Bugle, Trim | Top of head to point (overall length) | The head sits inside the material, so it forms part of the penetration depth |
| Pan, Round, Button, Truss, Cheese, Wafer, Pancake | Under the head to point | The head sits on the surface and adds nothing to penetration |
| Hex, Hex flange, Hex washer | Under the head to point | As above, the bearing face defines the start of the usable length |
| Socket cap (SHCS) | Under the head to point | Cylindrical head sits proud unless counterbored |
When in doubt, state the measurement basis explicitly on your drawing. We will confirm it back to you before cutting tooling.
| Product | Diameter range | Length range | Thread |
|---|---|---|---|
| Machine screws | M2 to M16 | 6 to 200 mm | ISO metric coarse and fine, fully threaded |
| Self tapping screws | Ø2.9 to 6.3 mm | 9 to 100 mm | Type A, Type AB, Type B |
| Wood screws | Ø3 to 8 mm | 12 to 150 mm | Coarse deep wood thread |
| Chipboard screws | Ø3 to 6 mm | 15 to 200 mm | Deep coarse full thread |
| Custom screws | To drawing | To drawing | Custom pitch, lead and length |
A complete callout has five parts. For example, M6 x 1.0 x 25 CSK Torx, zinc plated means:
Add the material and any standard reference, such as DIN 965 or ISO 7046, and the part is fully defined. See the DIN and ISO standards reference for the correct designation.
Sizes outside these ranges, non-standard pitches and made-to-drawing geometry are produced on our custom line. Send a drawing or a physical sample and we will confirm feasibility, tooling and lead time.
Send us your specification, finish and quantity. We reply within 24 hours with pricing and lead time. White-label and custom options available.
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