Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
ASME B32.100-2016 — Preferred Metric Sizes for Flat, Round, Square, Rectangular, and Hexagonal Metal Products
📐 ASME B32.100-2016 is the current core standard of the ASME B32 Committee on standardization of nominal sizes of metal and metal alloy wrought mill products. It establishes a unified series of preferred metric sizes and tolerances for flat, round, square, rectangular, and hexagonal metal products. Approved by ANSI on June 29, 2016, it revises the 2005 edition (R2011) and traces its lineage to B32.3M-1984 (flat products) and B32.4M-1980 (round, square, rectangular, and hexagonal products). The size series is built on the ISO 497 preferred-number system (series R5′, R10′, R20′), while tolerance data are drawn from ISO 4995, ISO 4997, ISO 1035-4, and ANSI B4.2.
💡 The purpose of B32.100 is “size rationalization”: it converges the commonly used metric sizes of five product forms into one orderly preferred series, so that products from different suppliers are interchangeable in design, combinable in inventory, and readily available from stock. It is the common language of the metal-material supply chain in the metric world.
1. Scope and Coverage 📌
Following five normative sections (Scope, General, Use of Tables, Basis of Tables, Tolerances), the standard presents 13 tables defining the preferred sizes for each product form:
| Product form | Dimensions specified | Typical size range | Tables |
|---|---|---|---|
| Flat products | Thickness, width, length | Thickness about 0.050–300 mm; width about 10–5000 mm | 1, 2, 3 |
| Round products | Diameter, length | Diameter about 0.020–320 mm | 4, 7 |
| Square products | Across-flat size, length | Across flat about 3–300 mm | 5, 7 |
| Hexagonal products | Across-flat size, length | Across flat about 1.5–150 mm | 6, 7 |
| Rectangular products | Section combination, length | About 1.6×10 to 100×200 mm | 8, 7 |
The standard does not force anyone to use these sizes: it explicitly does not preclude non-preferred sizes where precise engineering requirements dictate them. However, for general-purpose applications where latitude exists, the listed preferred sizes are encouraged because they promote interchangeability of metals in design, reduce inventories, and increase the availability of warehouse stock.
⚠️ B32.100 defines “nominal preferred sizes plus tolerances.” Not every listed size is produced in every metal and grade; availability and achievable tolerance combinations must be confirmed with producers or distributors.
2. Basis of the Preferred Size Series 📏
The preferred sizes follow the ISO 497 preferred-number logic with these progressions:
- Preferred sizes: successive values increase by about 60 percent (ISO 497 series R5′), the main series of choice.
- Second choice sizes: about 25 percent steps (series R10′), used only when no preferred size fits.
- Third choice sizes: about 12 percent steps (series R20′), used only when both higher-priority series fail.
Some deviations occur from rounding and from demonstrated or anticipated needs. The length series is usually a single preferred list without second choices. The selected sizes also reflect the actual sizes circulating in ISO and national standards of traditional metric countries, ensuring international compatibility. The size series itself originated in the 1974 approval under ANSI and has been refined through the 2005 and 2016 editions; the committee also maintains a formal process for interpretations, proposed revisions, and Cases, keeping the document responsive to industry needs.
💡 Selection rule: use a preferred size whenever possible, a second choice only if necessary, and a third choice only as a last resort. Off-series “custom sizes” multiply inventory and procurement cost unless truly unavoidable.
3. Tolerances and Referenced Standards 🔧
The 2016 edition retains the 2005 framework while deleting obsolete references, removing year dates from referenced standards, and adding data and clarification for para. 5.8 and Table 13. Tolerance data are adopted from established international or national standards:
| Table | Tolerance content | Reference basis |
|---|---|---|
| 9 | Thickness tolerances, hot-rolled steel sheet of structural qualities | ISO 4995 / ISO 5002 |
| 10 | Thickness tolerances, cold-rolled steel sheet of structural qualities | ISO 4997 |
| 11 | Tolerances, hot-rolled round, square, and hex steel bars | ISO 1035-4 |
| 12 | Tolerances, hot-rolled flat bars | ISO 1035-4 |
| 13 | Tolerances, cold-finished round, square, rectangular, and hex bars | ANSI B4.2 |
A size is fully defined only together with its tolerance. For cold-finished products, Table 13 and para. 5.8 together define how size-tolerance combinations are evaluated, an area clarified in this edition.
4. Engineering Practice Points 🛠️
- 🔍 Selection flow: identify the section form → choose the nearest preferred size from the corresponding table → fix the tolerance class per the material specification → confirm availability of that material-size-tolerance combination with the supplier.
- 📦 Inventory and purchasing: consolidating near-identical specifications onto preferred steps reduces stock keeping units; sharing one preferred size across projects unlocks volume-purchase advantages.
- 🔧 Tolerance check: the size tables and tolerance tables are referenced separately — an order must state both the nominal size and the tolerance basis (e.g., “Φ50 per ISO 1035-4”), never just the dimension.
- 🔄 Edition and errata: the standard becomes effective one year after issuance; the B32 Committee may publish Cases and Errata on its committee page (go.asme.org/B32committee), which should be checked before use.
- 📋 Interpretations: formal interpretations, revision proposals, and case requests must be addressed in writing to the B32 Committee Secretary; ASME accepts responsibility only for interpretations issued through its established procedures.
5. FAQ ❓
❓ Q: How do B32.100, B32.3M, and B32.4M relate?
A: B32.100 is the consolidated successor of the two: flat products (B32.3M) and round, square, rectangular, and hexagonal products (B32.4M) are merged into one document with an added tolerance section. New designs should reference B32.100-2016 directly.
A: B32.100 is the consolidated successor of the two: flat products (B32.3M) and round, square, rectangular, and hexagonal products (B32.4M) are merged into one document with an added tolerance section. New designs should reference B32.100-2016 directly.
❓ Q: Are the tabulated sizes mandatory?
A: No, but strongly encouraged. The standard explicitly permits off-series sizes; for general-purpose use, however, the preferred sizes deliver interchangeability, inventory, and stock-availability benefits.
A: No, but strongly encouraged. The standard explicitly permits off-series sizes; for general-purpose use, however, the preferred sizes deliver interchangeability, inventory, and stock-availability benefits.
❓ Q: Why do the tolerance tables reference ISO rather than an ASME-developed system?
A: To stay aligned with international and leading national metric material trade, the B32 Committee adopts recognized data from ISO 4995, ISO 4997, ISO 1035-4, and ANSI B4.2, ensuring authority and avoiding duplication.
A: To stay aligned with international and leading national metric material trade, the B32 Committee adopts recognized data from ISO 4995, ISO 4997, ISO 1035-4, and ANSI B4.2, ensuring authority and avoiding duplication.
❓ Q: How do I tell preferred, second choice, and third choice sizes apart?
A: Preferred is the main series (about 60% steps), second choice advances about 25%, third choice about 12%. Priority falls in that order — select downward only when the higher-priority series cannot satisfy the requirement.
A: Preferred is the main series (about 60% steps), second choice advances about 25%, third choice about 12%. Priority falls in that order — select downward only when the higher-priority series cannot satisfy the requirement.
❓ Q: How should the standard be used alongside material specifications?
A: B32.100 supplies the nominal size and the applicable tolerance class, while the material specification (for example an ASTM or ISO product standard) supplies the grade, mechanical properties, and any additional delivery conditions. A complete procurement description combines both: nominal size per B32.100 plus grade and property requirements per the material standard. This division of labor keeps the sizing system universal across metals.
A: B32.100 supplies the nominal size and the applicable tolerance class, while the material specification (for example an ASTM or ISO product standard) supplies the grade, mechanical properties, and any additional delivery conditions. A complete procurement description combines both: nominal size per B32.100 plus grade and property requirements per the material standard. This division of labor keeps the sizing system universal across metals.
