SCREWKING
Practical references for people who buy fasteners — what the documents mean, what the markings mean, and what to specify before you order.
Every part passes and it still will not fit. What worst case and RSS each assume — including why 0.27% is a model output, not a defect rate — and when changing the screw is the cheap fix.
Upset ratio guidance runs around 2.25–2.3 in one blow — guidance, not a standard. Microforming reports the achievable value falling to about 1.6. Less margin and more scatter as parts shrink.
A single-side coating of t adds 4t to pitch diameter. At 6h the upper deviation is zero, so the allowance has to be put on the drawing — and it surfaces on the first production lot, not at sample stage.
ISO 16047 starts at M3. Charpy needs a 16 mm shank. The decarburisation hardness method needs a 1.25 mm pitch. Four unrelated standards, one pattern — and what to ask once they run out.
Under EN 10204 there are four different inspection documents and they are not interchangeable. What each type gives you, which fields to check, and what to put in the purchase order.
A4-80 encodes two independent decisions: corrosion grade and strength. Buyers routinely change one while assuming they changed both.