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ASME B27.6-1972 (2017) — General Purpose Uniform Cross Section Spiral Retaining Rings
🔩 ASME B27.6-1972 (2017) is the ASME B27 series document that defines the complete general and dimensional data for general purpose uniform cross section spiral retaining rings. Originally approved as American National Standard ANSI B27.6 in 1972 and reaffirmed by ASME in 2017, it remains a current and widely applied reference for the design, manufacture, inspection, and procurement of shaft and housing retaining rings. A spiral retaining ring is wound spirally from a flat spring-steel band with a uniform cross section; once seated in a circumferential groove on a shaft or inside a housing bore, it forms a projecting shoulder that locates and retains bearings, gears, bushings, and other machine elements in automotive, agricultural, electric motor, power tool, and general machinery applications.
💡 Unlike conventional single-turn snap rings, a spiral retaining ring is wound in multiple coils around the circumference, distributing the axial load evenly and avoiding the stress concentration at the gap of a stamped ring. It is the better choice where high axial capacity and shock resistance are required.
1. Scope and Ring Types 📌
The Standard covers two series of general purpose uniform cross section spiral retaining rings, each divided into Light Duty and Heavy Duty types. The rings are intended for use with the nominal shaft and housing sizes listed and in grooves of the recommended dimensions given. Tables 1 through 4 provide complete dimensional data for the rings, grooves, and inspection gages of each type. Unless otherwise stated, all dimensions are in inches (para. 1.4).
| Type Designation | Function | Duty | Dimension Table | Typical Applications |
|---|---|---|---|---|
| 2A01 | External ring (shaft) | Light Duty | Table 1 | General locating, light axial retention |
| 2A02 | External ring (shaft) | Heavy Duty | Table 2 | Axial retention of heavy bearings, gears |
| 2B01 | Internal ring (housing) | Light Duty | Table 3 | Light retention of parts inside bores |
| 2B02 | Internal ring (housing) | Heavy Duty | Table 4 | Heavy retention in hydraulic cylinders, gearboxes |
Per para. 1.3, the rings are intended primarily for use with the recommended shaft, housing, and groove sizes, although the diameters may in certain cases be altered to suit a particular design. Any change must be made with care: the shaft or housing size must not be altered so far that the ring takes enough permanent set to fit loosely after assembly, and the groove diameter must not be altered so far that the ring fits loosely in the groove.
⚠️ Permanent set is the governing concept here: if the ring is over-stretched during installation or forced into an oversized groove, it yields plastically and can no longer provide reliable axial retention. Always prototype and test any deviation from the standard groove dimensions before full production.
2. Material and Mechanical Property Requirements 🔧
The Standard permits carbon spring steel and corrosion resistant steel. Carbon spring steel rings shall conform to the chemical composition of SAE 1070 to 1090 or AISI 1070 to 1090 (or equivalent), with hardness and tensile strength tied to material thickness. Corrosion resistant steel rings shall conform to SAE 30302 (or equivalent), with tensile strength of 175,000 to 250,000 psi over the thickness range from 0.008 in. upward.
| Material | Minimum Thickness (in.) | Rockwell Scale | Hardness | Tensile Strength (psi) |
|---|---|---|---|---|
| Carbon spring steel | 0.0067 | 15N | 85–90 | 269,000–299,000 |
| Carbon spring steel | 0.0142 | 30N | 68–73 | 255,000–285,000 |
| Carbon spring steel | 0.0213 | A | 72–78 | 221,000–251,000 |
| Carbon spring steel | 0.0433 | C | 43–49 | 211,000–236,000 |
| Corrosion resistant steel | 0.008 and up | 15N/30N/A/C | Varies with thickness | 175,000–250,000 |
Regarding finish, rings are furnished with a natural (as-processed) finish, unplated or uncoated, unless otherwise specified. Where corrosion-preventive treatment is required, plating or coating is applied as agreed between manufacturer and purchaser. Critically, where plated or coated rings are subject to hydrogen embrittlement, they must be baked for three hours at 375°F (about 190°C), or at other suitable times and temperatures, as soon as possible after the plating or coating operation.
🚨 High-hardness spring steel is extremely sensitive to hydrogen embrittlement. If electroplated rings are not baked after plating, they can crack suddenly during assembly or under load. Specify a bake-out requirement in your purchase specification and request process certificates.
3. Crimp, Removal Devices, and Geometric Quality 📏
The Standard lays down explicit structural requirements:
- Crimp: unless otherwise specified by the purchaser, these sizes are furnished uncrimped — 2A01 light external 0.500–1.500 in., 2A02 heavy external 0.469–0.688 in., 2B01 light internal 0.500–1.500 in., 2B02 heavy internal 0.469–0.750 in. All other rings are crimped.
- Removal notches or slots: 2A01 and 2B01 have notches in sizes 0.500–2.750 in. and slots in sizes 2.813–11.000 in.; 2A02 has notches in all sizes; 2B02 has notches in all sizes, with slots in sizes 2.813–11.000 in., to admit removal tools.
- Dish: the height difference across the ring faces (Fig. 1) is limited by radial wall thickness, e.g., 0.001 in. maximum for walls of 0–0.039 in., rising to 0.014 in. maximum for walls of 0.650–1.000 in.
- Misalignment: the leaves of the ring must lie over each other; maximum misalignment is 0.010 in. for sizes 0.375–0.984 in., 0.020 in. for 1.000–1.969 in., 0.045 in. for 2.000–5.905 in., and 0.070 in. for 6.000 in. and above.
- Edge radius: material edges shall be rounded to a radius of not less than T/8 and not more than T/4, where T is the ring thickness.
4. Inspection Methods and Assembly Precautions 🛠️
For inspection, the Standard provides the lateral deformation test: the ring is placed between parallel hardened and ground steel platens equipped with a deflection gage graduated in thousandths, loaded with ten (10) pounds, and the distance between the platens must not exceed the minimum recommended groove width F″. Parallelism requires that the outer side surfaces of the rings in the free state be parallel to each other. Ring thickness is measured under the 10-lb load at a location other than the ring ends or gap. Appendix I offers a recommended standard drawing format to keep drawings consistent with the standard data.
For assembly, the dominant failure modes of spiral rings are plastic deformation from over-expansion or over-compression, edge damage caused by inadequate groove chamfers, and warping from prizing with improper tools. Use dedicated pliers or cone-type applicators and never force a ring with a screwdriver.
💡 A four-step selection routine: ① choose Light or Heavy Duty from the axial load and shaft size; ② read the recommended groove diameter and groove width from the standard table; ③ check the free outside/inside diameter and thickness against the gage dimensions; ④ define crimp, removal-notch, finish, and bake-out requirements in the purchase order.
5. Engineering Practice Essentials 📋
- 🔍 Groove machining: groove diameter and width must follow the standard table; the groove bottom must be free of sharp corners and burrs — a small chamfer of about 0.005 in. helps prevent scraping of the ring during assembly.
- 🔧 Material selection: choose corrosion resistant steel (30302 type) for corrosive environments; carbon spring steel for general machinery; verify the usable temperature range for high- or low-temperature duty.
- 📊 Traceability: the 2017 reaffirmation keeps this edition current; always cite the full designation (B27.6-1972 (2017)) in procurement documents and request mill certificates for composition and hardness.
- 📐 Interchangeability: rings of the same type and nominal size share common groove and gage dimensions, so products from different suppliers are in principle interchangeable — still, run a sampling assembly check before full adoption.
6. Frequently Asked Questions ❓
❓ Q: How does B27.6 differ from the common stamped snap-ring standards?
A: B27.6 covers spiral retaining rings wound from flat strip in multiple coils, whereas conventional snap rings are single-turn stamped parts. Spiral rings distribute load evenly around the circumference and carry higher loads, but take slightly more axial space — the two are not directly interchangeable.
A: B27.6 covers spiral retaining rings wound from flat strip in multiple coils, whereas conventional snap rings are single-turn stamped parts. Spiral rings distribute load evenly around the circumference and carry higher loads, but take slightly more axial space — the two are not directly interchangeable.
❓ Q: Why does the Standard insist on baking at 375°F for three hours after plating?
A: Plating and pickling introduce atomic hydrogen into the high-strength spring-steel substrate, causing hydrogen embrittlement. Baking at 375°F (≈190°C) for three hours lets the hydrogen diffuse out and restores toughness — critical for thin, hard rings (e.g., 15N 85–90).
A: Plating and pickling introduce atomic hydrogen into the high-strength spring-steel substrate, causing hydrogen embrittlement. Baking at 375°F (≈190°C) for three hours lets the hydrogen diffuse out and restores toughness — critical for thin, hard rings (e.g., 15N 85–90).
❓ Q: What do the “gages” in the dimension tables mean?
A: Gages are the inspection dimensions used to verify the installed condition of a ring — for example, the free diameter of the ring and the height of the projecting shoulder when seated in the groove. They form the common acceptance basis for manufacturer and purchaser.
A: Gages are the inspection dimensions used to verify the installed condition of a ring — for example, the free diameter of the ring and the height of the projecting shoulder when seated in the groove. They form the common acceptance basis for manufacturer and purchaser.
🔍 Q: Since all dimensions are in inches, how should metric users apply this Standard?
A: B27.6 is an inch-series document; ASME B27.8M covers metric tapered-and-reduced rings, but for uniform cross section spiral rings metric users typically pass inch data through conversion. Convert inches to millimeters with full precision and label units explicitly, and never mix inch and metric values in one fit.
A: B27.6 is an inch-series document; ASME B27.8M covers metric tapered-and-reduced rings, but for uniform cross section spiral rings metric users typically pass inch data through conversion. Convert inches to millimeters with full precision and label units explicitly, and never mix inch and metric values in one fit.
