ASME B107.33M-2002 — Socket Wrenches, Impact (Metric Series)

28 10 月, 2026
ASME Standards

🔨 ASME B107.33M-2002 is a substandard of the ASME B107 family, Hand Tools and Accessories, covering detachable impact socket wrenches in the metric series. It defines the complete general and dimensional data and the performance requirements for these tools, together with test methods for evaluating that performance. Impact sockets are used with electric and pneumatic impact wrenches in high-frequency service such as automotive repair, heavy-equipment assembly, and steel-structure erection. The Standard works with ASME B107.4M (Driving and Spindle Ends for Portable Hand, Impact, Air, and Electric Tools) and ASME B107.17M (Gages, Wrench Openings, Reference) to complete the dimensional chain from the square drive interface to the socket opening. All dimensions are in millimeters.

💡 The key difference between impact sockets and ordinary hand sockets is the loading: every hammer blow is an instantaneous high load. Impact sockets are designed with different material selection, heat treatment, and wall thickness — they are not interchangeable products.

1. Scope and Classification 📌

The Standard covers detachable socket wrenches intended for impact use, classified as follows:

Type I — Sockets: single hexagon (6-point) and double hexagon (12-point) openings for ordinary nut and bolt tightening.
Type II: reserved for future use.
Type III — Universal Sockets: single hexagon and double hexagon types with a universal joint for awkward, misaligned tightening positions.

Data tables are provided for five square drive sizes — 6.3 mm, 10 mm, 12.5 mm, 20 mm, and 25 mm — corresponding to the customary 1/4 in., 3/8 in., 1/2 in., 3/4 in., and 1 in. drives.

Square Drive	Corresponding Customary	Opening Types	Typical Applications
6.3 mm	1/4 in.	6-point / 12-point	Miniature impact work, tight spaces
10 mm	3/8 in.	6-point / 12-point	Light- and medium-duty impact wrenches
12.5 mm	1/2 in.	6-point / 12-point	General impact work, most common size
20 mm	3/4 in.	6-point / 12-point	Heavy trucks and large equipment repair
25 mm	1 in.	6-point / 12-point	Large impact wrenches, heavy industry

2. Material, Heat Treatment, and Marking Requirements 📏

Section 4 defines the product requirements:

Materials: unless otherwise specified, the tool material shall be steel, whose chemical composition and heat treatment must produce tools meeting all requirements of this Standard (proof torque and impact resistance).
Dimensions: key socket dimensions (square drive hole, opening across flats, depth) must conform to the applicable data tables; hexagon mandrel dimensions and maximum depth of mandrel insertion are specified to be consistent with the wrench-opening gages.
Marking: sockets must be marked plainly and permanently with the manufacturer’s name or a trademark of known character so the source and country of origin can be determined, and with the nominal size of the wrench opening (distance across flats) — e.g., 17, 19, 21 — for rapid selection on the job.

⚠️ Marking is not decoration: in impact work, operators select sockets quickly behind goggles and gloves, so a legible across-flats size is directly tied to correct selection and productivity. Products with missing or illegible marking must be rejected.

3. Performance Requirements: Proof Torque and Hardness 🔬

Two core performance requirements are defined:

Proof torque: when tested as specified, sockets must withstand the proof torque given in the applicable tables without failure or permanent deformation (set) that could affect durability or serviceability. The proof torque verifies load capacity and material strength margin.
Hardness: Rockwell hardness per ASTM E 18, ensuring heat treatment places the material in a range that is strong enough yet tough enough — too hard invites brittle fracture, too soft invites deformation.

💡 The “proof torque” of impact sockets differs from that of hand sockets: it must survive the high-frequency hammering fatigue and transient peak loads of an impact wrench. When buying, check that the product cites this Standard and is impact (not ordinary hand) series.

4. Test Procedures 🧪

Section 5 defines the test procedures:

Dimensional inspection: check opening size and square-drive fit with hexagon mandrels and gages under specified conditions.
Proof torque test: apply the tabulated torque with the prescribed loading arrangement (avoiding test-fixture clamping damage to the specimen) and check for failure and permanent deformation.
Hardness test: measure Rockwell hardness per ASTM E 18 and compare with the specified range.

5. Engineering Practice and Safety 🛠️

🔍 Size matching: the square drive must match the impact wrench output, and the opening across flats must match the fastener; cross-series approximations (e.g., 12.5 mm on a nominal mismatch) are not recognized in the metric series.
🔧 Never mix hand sockets with impact work: ordinary chrome hand sockets must not be used with impact wrenches — they can shatter instantly; impact sockets may be used for low-speed hand tightening but should not be repeatedly torqued without impact loads.
📊 Wear inspection: check regularly for worn or deformed openings, excessive square-hole wear, and cracks; discard any socket with cracks or distortion.
📋 Universal sockets: Type III universal sockets lose load capacity at large deflection angles; keep the angle small and do not load at maximum deflection.

🚨 Impact sockets fatigue under high-frequency hammering: a visible crack usually means imminent fracture. Inspect before work, use conforming products, and always wear eye and hand protection during impact operations.

6. Frequently Asked Questions ❓

❓ Q: Why must ordinary hand sockets not be used with impact wrenches?
A: Hand sockets are designed for static torque with little toughness reserve; under the high-frequency transient loads of hammering they crack and fly apart easily. Impact sockets are designed with impact-rated material and heat treatment and must not be interchanged.

❓ Q: How does B107.33M relate to the inch-series impact sockets?
A: B107.33M covers the metric series (mm units, 6.3–25 mm drives); the companion inch series (1/4–1 in. drives with inch-denominated openings) is covered by another B107 standard. Choose the series by the fastener system you work with.

❓ Q: What does the across-flats marking on a socket mean?
A: It is the distance between two parallel faces of the opening (e.g., 17 means 17 mm), matching the across-flats size of the bolt/nut head; it enables fast selection and is a mandatory marking.

🔍 Q: Can a socket that failed the proof torque test still be used?
A: No. The proof torque verifies basic capability to carry impact loads; failure indicates material, heat treatment, or dimension design deficiencies that could cause deformation or failure in service. It must be rejected.