Socket Size Chart: Metric, Imperial & Drive Guide

Use this socket size chart to find the right socket for the job — whether you're working in metric or imperial, with a 1/4", 3/8" or 1/2" drive. Select your drive size, find your fastener, and confirm whether you need a standard (shallow) or deep socket. Getting the size right avoids rounding fastener heads and keeps the job moving.

How Socket Sizes Work

Socket sizes refer to the across-flats measurement of the fastener head — the same dimension used for spanners and open-end wrenches. A 19mm socket fits a fastener with 19mm across the flats, regardless of whether the fastener itself is metric or has a metric thread.

Drive size is separate from socket size. It refers to the square drive on the ratchet or extension bar that connects to the socket — 1/4", 3/8" or 1/2". A 3/8" drive 13mm socket and a 1/2" drive 13mm socket both fit the same nut, but the larger drive handles more torque.

Standard (shallow) sockets work for most fasteners. Deep sockets are needed where the fastener shank protrudes through the nut — common on wheel studs, bolts with long thread engagement, and spark plugs.

Metric Socket Size Chart — 1/4" Drive

A 1/4" drive is suited to light work: electronics, small engines, interior trim, and torque-sensitive applications. Typical range is 4mm–15mm. Handles up to approximately 35 Nm.

Metric Socket Size Chart — 3/8" Drive

A 3/8" drive covers the widest general-purpose range — from 8mm up to 24mm in most sets. The right choice for most automotive, machinery, and workshop tasks. Handles up to approximately 100–135 Nm.

Metric Socket Size Chart — 1/2" Drive

A 1/2" drive is for heavy work: wheel nuts, suspension components, heavy machinery, and high-torque fasteners. Standard range is 17mm–50mm. Handles 200 Nm and above depending on the tool.

Imperial (SAE) Socket Size Chart

Imperial sockets are sized in fractions of an inch and are common on American-manufactured vehicles and equipment, agricultural machinery, and older plant. The sizing convention follows SAE (Society of Automotive Engineers) standards. Available in 1/4", 3/8" and 1/2" drive.

Metric to Imperial Socket Conversion Chart

No exact metric-to-imperial match exists — socket sizes are based on different measurement systems. The table below shows the closest imperial socket to each common metric size. In most cases the fit will be too loose for torquing; use the correct metric socket where precision matters.

Standard vs Deep Socket Guide

Standard (shallow) sockets handle the vast majority of work. Deep sockets are needed when the bolt shank extends through the nut, leaving the socket unable to seat properly on a shallow socket. Common applications for deep sockets include wheel studs, exhaust bolts, spark plugs, and any application where thread is exposed above the nut.

Choosing the Right Drive Size

Drive size determines torque capacity and tool compatibility. Match the drive to the job — using a 1/2" drive on small fasteners risks overtorquing and rounding; using a 1/4" drive on large fasteners risks snapping the drive or the socket.

Frequently Asked Questions

What is the most common socket size?
In metric, 10mm is the most frequently used socket size — it fits M6 bolt heads which appear on engines, brackets and interior components across virtually every vehicle and machine. In imperial, 3/8" and 7/16" are among the most common SAE sizes.

What's the difference between metric and SAE (imperial) sockets?
Metric sockets are sized in millimetres and fit metric fasteners. SAE sockets are sized in fractions of an inch and fit imperial fasteners. You can sometimes use one in place of the other on a loose fit, but this risks rounding the fastener head. Always use the correct socket type for the fastener system you're working with.

What size socket fits a 1/2" bolt?
A 1/2" bolt (half-inch diameter) typically has a 3/4" hex head, so you need a 3/4" socket. Note that bolt diameter and socket size are different measurements — the socket fits the hex head, not the shank.

Can I use a metric socket on an imperial fastener?
In some cases yes — where the metric size is very close to the imperial size. For example, an 11mm socket is almost identical to a 7/16" (11.1mm). However, for torqued fasteners, always use the matching socket to avoid rounding. The closest metric-to-imperial matches are shown in the conversion chart above.

What is a 19mm socket equivalent to in imperial?
A 19mm socket is equivalent to 3/4" (19.05mm). The difference is only 0.05mm, making it one of the closest metric-imperial equivalents. A 3/4" socket will fit a 19mm fastener on a light fit but use the correct metric socket for torqued work.

When do I need a deep socket?
Use a deep socket when the bolt shank protrudes through the nut, preventing a standard socket from seating properly. Common applications include wheel studs (where the thread extends past the wheel nut), spark plugs, and long threaded rod assemblies. If a standard socket rocks or won't engage the full depth of the hex, switch to a deep socket.

What's the difference between 6-point and 12-point sockets?
A 6-point socket has six internal contact points and grips the flat sides of the hex fastener. It's less likely to round worn or corroded fasteners and is the preferred choice for high-torque work. A 12-point socket has twelve contact points, allowing it to engage the fastener at more angles — useful in tight spaces where swing is limited. For general use, 6-point is the better choice.

What does 3/8" drive mean?
The drive size refers to the square post on your ratchet or extension bar that connects to the socket — not the socket size itself. A 3/8" drive means the square post is 3/8" across. Different drive sizes have different torque capacities: 1/4" for light work, 3/8" for general use, 1/2" for heavy-duty applications. Sockets and ratchets must share the same drive size to connect.