Overview
ISO 20318-2:2019 - Mechanical pencils and leads for general use - Part 2: Black leads specifies classification, dimensions, quality criteria and test methods for black leads (graphite cores) intended for mechanical pencils used in general writing. The document complements ISO 20318-1 (mechanical pencils) and defines measurable requirements for lead diameter, length, bending strength and hardness/density evaluation to promote compatibility and consistent quality across manufacturers.
Key topics and technical requirements
- Classification: Leads are classified by hardness degree (e.g., 9H … 6B, with HB as the median) and by marking diameter (nominal sizes such as 0.2, 0.3/0.35, 0.5, 0.7, 1/0.9, 1.3, 1.4, 2 mm).
- Dimensions: Specified ranges for actual lead diameters (see Table 4 in the standard). Typical recommended lengths: (60 ± 1) mm for 0.2–1.4 mm leads and (130 ± 1) mm for 2 mm leads, unless otherwise agreed.
- Bending strength: Minimum bending strength values are defined per marking diameter and hardness degree (sample: 10 leads). The bending test applies a centrally placed load at a constant rate (10 mm/min) and computes strength from the measured fracture load using the standard formula (σ = 8 F l / (3 π d^3)). Test fixture geometry (anvil radius, span) is specified.
- Hardness degree and writing density: Because there is no single scientific definition of "hardness degree," the standard requires both quantitative (writing density measured with a densitometer using line-drawing devices - recording or spiral types) and qualitative (handwriting comparison) assessments. Test conditions (temperature, relative humidity), line-drawing loads, speeds and sampling (five leads) are defined to ensure reproducible density measurements.
- Test conditions and procedures: Environmental conditions, sample sizes, measurement points and device parameters are standardized to support consistent laboratory testing.
Applications and who uses it
- Manufacturers of mechanical pencil leads and stationery seeking to certify product dimensions, mechanical strength and writing characteristics.
- Quality control and test laboratories performing bending strength and writing-density tests.
- Product designers and compatibility engineers ensuring pencil/lead interchangeability across brands.
- Procurement specialists and retailers requiring conformance evidence for specification and labeling.
- Standards bodies and conformity assessors referencing harmonized test methods.
Related standards
Keywords: ISO 20318-2:2019, mechanical pencils, black leads, classification, dimensions, bending strength, hardness degree, writing density, test methods.
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