SAE Socket Sizes

GEARWRENCH’s current sets show 1/4-in. drive SAE sockets around 5/32 to 9/16 in. and 1/2-in. drive SAE sets around 3/8 to 1-1/2 in., demonstrating the overlap between drive families rather than fixed boundaries.

Metric Socket Sizes

GEARWRENCH currently sells 1/4-in.-drive metric sockets around 4 to 15 mm, while one current 1/2-in.-drive set extends to 36 mm. Commercial ranges vary by manufacturer and product line.

A socket is a removable wrenching tool that fits over a fastener head or nut, engages its flats or points, and connects to a ratchet, breaker bar, torque wrench, impact wrench, or other drive tool. Main applications include construction, automotive repair, machinery, equipment maintenance, fabrication, and assembly.

A “1/2-in. drive by 19 mm socket” means a 1/2-in. ratchet interface paired with a 19 mm fastener opening. These two numbers describe entirely different parts of the same tool.

For ordinary hex fasteners, socket opening approximately equals the fastener’s width across flats, subject to standardized tool clearances and tolerances. ASME B107.17 establishes gages and mandrels for wrench-opening dimensions in common inch and metric sizes, providing the technical basis for how these openings are verified.

Conversions use the exact factor 1 in. = 25.4 mm. A converted metric dimension should not be treated as an automatic acceptable substitute for the correctly marked SAE socket.

Nearest SAE size is a dimensional comparison, not a guaranteed safe substitute. This satisfies a major search intent while making the limitation clear.

3/8 in. equals 9.525 mm, with a nearest common metric size of 10 mm, a difference of 0.475 mm. 3/4 in. equals 19.05 mm, with a nearest common metric size of 19 mm, a difference of only 0.05 mm. This shows why some SAE/metric pairs are much closer than others.

Use this table for quick identification when working with metric hardware in the U.S., where SAE tools are also on hand.

Sometimes the dimensions are very close, but substitution can create excessive clearance, round the fastener, slip under high torque, or damage corroded fasteners. Use the correctly marked socket whenever possible; nearest-equivalent charts are for identification and reference, not automatic substitution. Especially avoid loose substitutions on high-torque bolts, damaged fasteners, impact tools, and precision assemblies.

GEARWRENCH’s current 1/4-in.-drive sets include approximately this SAE and metric range. This is a product-market range, not a mandatory ASME size boundary.

3/8-in. drive commonly overlaps both the smaller 1/4-in. drive range and the larger 1/2-in. drive range, which is part of why it is often considered the most versatile general-purpose drive size. There is no one universal maximum socket opening for this drive size; exact coverage depends on the manufacturer and product line.

Current GEARWRENCH examples fall in this approximate range. Typical applications include larger automotive fasteners, suspension work, structural or equipment hardware, and higher-torque assembly, but drive size does not map to a universal torque rating.

Typical contexts include heavy equipment, trucks, large structural fasteners, and industrial maintenance. Larger drives permit larger ratchets and breaker bars, larger sockets, and heavier overall tool construction, but actual permissible torque comes from the specific tool manufacturer’s rating, not merely from the square-drive dimension itself.

Selection depends on socket opening size, required torque, access, ratchet or tool dimensions, available drive tools, and whether the work is impact or hand-tool based.

A 6-point socket has six engagement points at 60-degree spacing. A 12-point socket is a double-hex design with points every 30 degrees. A 12-point socket fits an ordinary 6-point fastener, but for a 6-point fastener under substantial force, 6-point geometry generally provides better matching and contact with lower slip risk.

Modern sockets often use radiused or off-corner engagement. Manufacturer literature explains that six-point sockets apply force to the fastener’s flat sides rather than its more fragile corners, reducing the tendency to round the fastener, particularly under high torque or on stubborn, corroded hardware.

A shallow socket has a shorter overall length, works well where clearance is limited, and fits ordinary bolt heads or nuts without long protruding studs. Manufacturers currently offer families in shallow, semi-deep, and deep forms, alongside standard, mid-length, and low-profile variants, but exact lengths are product-specific rather than fixed by one universal dimension.

A deep socket has a full-length internal well providing clearance over long threaded studs. Do not assume all manufacturers use identical deep-socket lengths; these ranges are representative examples, not a fixed industry standard.

ASME B107.110 provides performance and safety requirements for socket wrenches and related components. Ordinary chrome hand sockets should not be used on impact guns, since they are not designed for the sudden rotational shock loading that impact tools generate.

Manufacturer product families currently sell impact sockets in shallow, semi-deep, deep, 6-point, and 12-point configurations, so use manufacturer-supported ranges as examples rather than an absolute limit.

Chrome hand sockets often use smooth chrome-plated exteriors for corrosion resistance. Impact sockets may use Cr-V, Cr-Mo, Ni-Cr-Mo, or phosphate-finished alloy steels depending on the manufacturer and design; not every impact socket is necessarily Cr-Mo, so the specific product’s material and finish should be confirmed rather than assumed.

A socket fits the head or nut’s across-flats dimension, not the nominal bolt shank diameter. A 3/4-in. bolt, for example, has a standard hex head across flats of 1-1/8 in., which is the socket size actually needed, not 3/4 in. For the complete bolt dimensional reference, see the Hex Bolt Size Chart.

A standard hex bolt and a heavy-hex structural bolt with the same nominal bolt diameter can use different socket sizes because their heads have different widths across flats. This distinction matters directly for readers working with ordinary hex bolts, structural heavy-hex bolts, and anchor systems. For head-width data across both types, see the Hex Bolt Size Chart, for strength and grade markings see the Bolt Grade Chart, and for anchor-specific dimensions see the Anchor Bolt Size Chart.

For the same properly standardized external hex fastener, the nominal socket opening and wrench opening are generally the same across-flats size. A 19-mm hex head uses both a 19-mm wrench and a 19-mm socket. However, socket and wrench body geometry and clearance differ, since a socket surrounds the fastener while a wrench engages from the side, which affects access in different situations.

Two sockets with the same opening can have different wall thickness, outside diameter, and overall length. This matters in recessed bolt holes, tight engine bays, equipment, and fasteners close to walls or other obstructions. This page does not publish one universal outside diameter by socket opening, since that dimension is tied to a specific product line rather than a single across-the-board standard.

An adapter does not give the smaller socket or tool the strength capacity of the larger drive; the weakest link in the chain still governs overall capacity. Universal-joint and swivel impact sockets provide angled access for hard-to-reach fasteners, with detailed joint-angle specifications varying by product.

Spark plug sockets have specific depths, retention features, and specialized openings distinct from ordinary deep sockets. Possible common openings include 5/8 in. and 13/16 in., along with metric and specialty thin-wall sizes depending on plug design. Do not assume two sizes cover every spark plug; the exact socket needed should be confirmed against the specific plug. ASME’s socket-wrench standard consolidated multiple earlier socket standards, including prior spark-plug socket requirements, into the current combined ASME B107.110 standard.

Current ASME B107.110-2019 establishes performance and safety requirements for sockets, wrench handles, nutdrivers, and related attachments, and it consolidated several earlier B107 standards into one combined document. Standardized dimensions do not imply every listed size must be stocked by every manufacturer; ASME explicitly notes that users should consult manufacturers for actual stock production sizes and lengths.

Current ASME B107.17-2020 (R2025) establishes final-inspection gage sizes and test-mandrel sizes for common inch, metric, and spark-plug wrench openings, providing the dimensional verification framework behind the socket sizes referenced throughout this page.

Socket opening size does not establish one universal torque capacity. Capacity depends on drive size, opening size, socket geometry, point count, alloy and heat treatment, and hand versus impact design. Manufacturer literature indicates current hand sockets are proof-tested relative to ASME B107.110 requirements, with some product families rated above the minimum standard proof torque. This page does not publish a generic “3/8 drive equals X ft-lb maximum” table unless tied to an exact tool standard or product, since doing so would misrepresent capacity that is actually product-specific.

Possible specialty forms include square fasteners, 8-point, external Torx and E-Torx, spline, and other specialty automotive or industrial forms. These require matching specialty sockets rather than an ordinary hex socket, and should not be confused with standard hex openings covered on this page.