D1 Mini Refill vs. Lead Hardness Scale
Comparing 2 standards across 12 specifications. 12 key differences identified.
The D1 Refill (standardized under ISO 12757-1 as Type D) is a standardized miniature metal-cased ballpoint/gel refill measuring exactly 67.0 mm in length and 2.35 mm in diameter. Friction-fit into internal selector sleeves, it is the universal standard for multi-function pens (3-in-1, 4-in-1), compact pocket pens, and precision stylus combinations.
The Graphite Hardness Grading Scale (standardized under ISO 15184 and ASTM D3363) classifies pencil graphite from 9H (hardest, lightest grey, highest clay content) through HB (medium equilibrium) to 9B (softest, darkest black, highest graphite content). HB is the universal writing standard and the exact equivalent to the North American No. 2 pencil.
Specification Comparison Table
12 Parameters| Parameter / Spec | ||
|---|---|---|
|
Overall Length
|
67.0 ± 0.5 mm (2.64 in) | — |
|
Outer Tube Diameter
|
2.35 ± 0.05 mm (0.093 in) | — |
|
Mounting Mechanism
|
Friction-fit slide sleeve (no threads or springs attached to refill body) | — |
|
ISO Standard Code
|
ISO 12757-1 Type D | — |
|
Ink Varieties
|
Hybrid low-viscosity (Uni Jetstream SXR-200), Gel (Zebra JSB), standard ballpoint (Lamy M21, Schmidt 635) | — |
|
Benchmark Multi-Pens
|
Lamy 2000 4-Color, Rotring 600 3-in-1, Zebra Sharbo X, Kaweco Liliput ballpoint | — |
|
Hard Grade Range (9H to 2H)
|
— | 9H, 8H, 7H, 6H, 5H, 4H, 3H, 2H — high clay/polymer binder ratio, crisp hairline precision, zero smudging |
|
Medium Equilibrium Range (H, F, HB, B)
|
— | H (Hard), F (Fine point retention), HB (Hard Black — standard writing balance), B (Black) |
|
Soft Grade Range (2B to 9B)
|
— | 2B, 3B, 4B, 5B, 6B, 7B, 8B, 9B — high graphite content, deep velvety blacks, artistic shading |
|
US No. 2 Pencil Equivalent
|
— | HB grade (mandatory for optical Scantron standardized bubble test optical scanners) |
|
US Numbering System Cross-Check
|
— | #1 = B | #2 = HB | #2.5 = F | #3 = H | #4 = 2H |
|
Origin
|
— | Developed by Joseph Hardtmuth of Koh-i-Noor in Vienna (1790s), who introduced the H/B alphanumeric system |