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, passivated
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 |
| Pickled | Finish | Pickling (acid descaling) |
⚠️ 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.
- Lower case (6g) = external thread (bolt)
- Upper case (6H) = internal thread (nut or tapped hole)
The usual commercial pairing is 6g / 6H. The external thread is limited on the oversize side and the internal thread on the undersize side, so that assembly is assured.
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.