ASME B107.3-1978 — Socket Wrenches, Power Drive (Non-Impact), Inch Series

28 10 月, 2026
ASME Standards

🔩 ANSI/ASME B107.3-1978 is the American National Standard covering the complete general and dimensional data for detachable socket wrenches for power drive use as distinguished from impact drive, expressed in the inch (U.S. Customary) series. These sockets are used with electric and pneumatic power tools whose output is continuous rotational torque rather than the pulsed impacts of an impact wrench — a distinction that imposes dedicated requirements on opening accuracy, hardness, and toughness. The Standard was developed under the B107 “Socket Wrenches and Drives” committee (later reorganized as “Hand Tools and Accessories”) with the ASME secretariat and major contributions from the Hand Tools Institute; it was approved by ANSI on November 8, 1978 and issued on February 15, 1979.

💡 The key to understanding B107.3 is the word “non-impact”: it addresses continuous torque from power tools, not the pulsed loads of impact tools. Impact sockets must be selected to the dedicated impact socket standards — never interchange the two.

1. Scope and Classification 📌

The Standard covers the complete general and dimensional data for detachable socket wrenches for power drive use, distinguished from impact drive. As in other B107 standards, inclusion of dimensional data does not imply that all described products are stock production sizes — consumers should consult manufacturers. Five classes are defined by construction and application:

Class 1: Sockets, single hexagon (6 point) and double hexagon (12 point) — Style A (regular length) and Style B (long length).
Class 2: Sockets, square (4 point) and double square (8 point).
Class 3: Universal sockets, block type, single and double hexagon.
Class 4: Universal sockets, ball joint type, single and double hexagon.
Class 5: Sockets for self-tapping screws — Style A (regular length) and Style B (long length).

⚠️ The dimensions and hardness in this Standard target non-impact power drive service. Using a non-impact socket on an impact wrench subjects it to impact loads that can tear the opening, propagate cracks, or even burst the socket; conversely an impact socket works on non-impact tools but sizes must be verified. Always match the socket type to the tool.

2. Material, Hardness, and Marking 🛡️

Section 4 of the Standard specifies material, hardness, marking, and finish requirements:

Material: materials used in manufacture shall produce sockets conforming to the specified requirements (typically forged alloy steel).
Hardness: sockets, except Class 5, shall be hardened and tempered to a Rockwell hardness of not less than 40 nor more than 56 on the “C” scale; Class 5 (self-tapping screw) sockets shall be hardened and tempered to 55–65 HRC or case-hardened to an equivalent hardness.
Marking: sockets shall be marked plainly and permanently with the manufacturer’s name or trademark, and with the size of the wrench opening (distance across flats), ensuring traceability.
Finish: all external surfaces free from pits, nodules, forge flash, burrs, and cracks; forge flash completely removed and blended smoothly with adjacent surfaces.
Coatings: one of the specified rust-preventive systems, e.g., hot phosphating (heavy chemically produced phosphate coating followed by rust-preventive oil).

Class	Hardness Requirement	Typical Features
Class 1–4	40–56 HRC (hardened and tempered)	Hexagon, double-hex, square, universal construction
Class 5	55–65 HRC or equivalent case hardening	Self-tapping screw gripping openings

3. Design Essentials 📐

The Standard imposes several specific construction requirements:

Wrench opening: bolt and nut opening tolerances shall ensure acceptance when gauged with gauges conforming to FED-STD-346 (Gauging, Wrench Openings), assuring a proper fit on standard fasteners.
Bolt clearance hole: provided in all sockets except Classes 3, 4, and 5 — minimum depth not less than 1.5 times the minimum depth of the nut opening for regular-length sockets, and not less than 70% of overall length measured from the wrench-end face for long-length sockets; a through hole with minimum diameter equal to 50% of the square drive size or the bolt clearance hole diameter, whichever is smaller.
Female drive opening: all female drive openings shall be broached, punched, machined, or formed smooth and well-defined, with dimensions conforming to ANSI B107.4 (later B107.4M).
Countersink: except for Class 5, the nut-end opening shall be countersunk with an included angle of 90 to 150 degrees and a minimum diameter equal to the across-corners dimension, easing placement over the nut.
Universal joints: Class 3 block and Class 4 ball joint universal sockets shall have joints that flex freely without excessive play, to the dimensions in the corresponding tables.

🚨 Non-impact power sockets develop fatigue cracks under sustained torque. Inspect openings and bores for cracks, wear, or distortion before each use and discard any cracked socket immediately. At high tool speeds a bursting socket can eject fragments — wear eye protection and stay within the rated speed.

4. Dimensional Data and Test Procedures 📊

The Standard presents extensive figures and tables (Figures 1–4; Tables 1–16) covering, for each square drive size (1/4, 3/8, 1/2 in, etc.), the across-flats opening sizes, lengths, wall thicknesses, drive opening dimensions, universal construction dimensions, and the hexagon and square mandrel dimensions with maximum insertion depth (Tables 15 and 16) used to verify openings and fits. Test procedures (Section 5) cover opening go/no-go gauging per FED-STD-346, hardness testing per ASTM E18 (Rockwell), and dimensional conformance checks.

Square Drive Size	Typical Opening Range (across flats)	Applicable Classes
1/4 in drive	1/4 to 9/16 in (6/12 point)	Class 1, 2, 5
3/8 in drive	3/8 to 3/4 in (6/12 point)	Class 1, 2, 3, 4, 5
1/2 in drive	7/16 to 1-1/8 in (6/12 point)	Class 1, 2, 3, 4, 5

5. Engineering Practice Essentials 🛠️

🔍 Selection: confirm the power tool type (non-impact) and square drive size, then choose the opening size by fastener size; use 12-point or long sockets in tight spots and universal sockets where angular access is needed.
🔧 Use: seat the socket fully on the nut before starting the tool; for continuous-torque non-impact tools, control speed and load duration, and allow cooling in heavy-duty applications.
📋 Maintenance: clean and rust-protect after use; periodically check openings for wear (worn openings slip and round off fastener corners) and gauge them per FED-STD-346.
📊 Procurement: verify marking (manufacturer and opening size), hardness reports, and wrenches-opening gauge records.

6. Frequently Asked Questions ❓

❓ Q: What is the difference between B107.3 sockets and impact sockets?
A: B107.3 covers non-impact (continuous torque) power drive sockets hardened 40–56 HRC with relatively lighter walls. Impact sockets are built for pulsed impact loading with a different hardness/toughness balance and thicker walls, per the dedicated impact socket standards.

❓ Q: Can B107.3 sockets be used on an impact wrench?
A: No. Impact loads far exceed the design capacity of non-impact sockets, causing opening cracks, splitting, or even bursting with injury risk. Impact service requires impact-rated sockets.

🔍 Q: What are the trade-offs between 12-point and 6-point sockets?
A: A 12-point (double hex) socket indexes at smaller angles for easier access in confined spots, but at equal torque it concentrates contact stress and can round fastener corners more easily; for high-strength fastening, prefer 6-point sockets.

❓ Q: Why must the female drive opening conform to B107.4?
A: B107.4 standardizes driving and spindle end dimensions for portable hand, impact, air, and electric tools, ensuring interchangeability between sockets and power tool drive squares from different manufacturers — the basis of power tool interface standardization.

ASME B107.3-1978.pdf