Reading a Screw Designation — What M4 × 0.7 × 10 Means
Breaking down the fastener callout on a purchase order or drawing, item by item.
Suppose a purchase order reads:
Cross recessed pan head machine screw M4 × 0.7 × 10, STS304, A2-70, acid cleaned
Read in order, each element means the following.
| Element | Meaning | Explanation |
|---|---|---|
| Cross recessed | Drive type | Phillips. Others: slotted, hex socket, combination (±) |
| Pan head | Head type | Others: flat countersunk, truss, binding, hex |
| Machine screw | Product type | Fastened into a pre-tapped female thread |
| M4 | Nominal diameter | Male thread outside diameter 4 mm (actual is smaller by the tolerance) |
| 0.7 | Pitch | 0.7 mm between adjacent thread crests |
| 10 | Length | 10 mm. Whether the head is included depends on head type (see below) |
| STS304 | Material | KS designation. SUS304 in JIS |
| A2-70 | Property class | Minimum tensile strength 700 N/mm² |
| Acid cleaned | Finish | Our 산처리: degreasing and washing, then a chemical brightening treatment (separate from passivation) |
STS304 is the steel grade of the material; A2-70 is the property class of the finished fastener. The same STS304 material can end up in different property classes depending on the manufacturing process and the degree of work hardening, so check each separately (A2-50, A2-70, A2-80 — what is the difference?).
⚠️ Length is measured differently by head type
This is where ordering mistakes most often occur.
| Head type | Length datum |
|---|---|
| Pan, truss, binding (head sits above the surface) | From under the head to the tip |
| Flat countersunk (head sits fully flush) | From the top of the head to the tip (overall length) |
| Raised (oval) countersunk | From the line where the raised dome meets the countersunk cone, to the tip |
Raised countersunk heads are easily confused with flat countersunk ones. The datum is not the top of the dome but the line where the raised portion ends and the countersunk cone begins — in effect, only the depth that sits inside the surface is counted.
The same "10 mm" therefore includes the head on a countersunk screw. If the drawing and the purchase order use different data, you will receive a different part.
What do 6g and 6H mean?
A suffix such as M4 × 0.7 - 6g is the thread tolerance class (ISO 965-1). The number 6 is the tolerance grade; the letter g or H is the tolerance position.
- Lower case (6g) = external thread (bolt). The tolerance zone lies below the basic size
- Upper case (6H) = internal thread (nut or tapped hole). The lower limit of the tolerance zone is at the basic size
The usual combination is 6H/6g (6H internal, 6g external), which sets the permissible dimensions so that the two threads mate properly.
The same name can follow different standards
Even a "cross recessed pan head machine screw" can differ in head dimensions or tolerances depending on the standard applied — KS, ISO, JIS or a customer's own specification. The Korean KS annex dimensions used domestically differing from ISO dimensions is a typical case. A formal specification therefore includes the applicable standard number.
| First enquiry | Confirm before production or final order |
|---|---|
| Head type, nominal diameter × length, material, finish | Applicable standard number, detailed drawing, pitch, tolerance, property class, finish conditions |
Head type, nominal diameter × length, material and finish — four items are enough for us to identify the part. Pitch can be omitted for coarse threads; include the property class if it matters. If you do not know the part number, simply describe the specification in a quote request and we will find it for you. Before production or a final order, the applicable standard and quality requirements are confirmed as well.
References
- ISO 261:1998 ISO general purpose metric screw threads — General plan — coarse pitch by size (M4 = 0.7)
- ISO 965-1:2026 ISO general purpose metric screw threads — Tolerances — Part 1: Principles and basic data — tolerance grades and positions, 6H/6g designation
- KS B 1023:2016 Cross-recessed machine screws — head styles and dimensions, including the non-ISO Korean shapes in the annex (truss, binding, etc.)
- ISO 7046-2:2011 — cross-recessed countersunk flat head screws (steel 8.8, stainless A2-70, non-ferrous); overall length including the head
- ISO 7047:2011 — cross-recessed raised countersunk head screws; length excludes the raised dome
Last revised 2026-10-09