Metric(mm) vs Standard(SAE) Socket Size Conversion

By: Leon Rhodes

Sockets are available in metric and standard sizes but what if you need to switch between the two measurement systems? Why is one socket too small while the next is too loose? Argh! I get it and the 33mm socket is most frustrating, here is what you need to know.

What a 33mm Socket is in Standard Size

Standard sockets that work on Metric bolts (chart)

This socket conversion chart tells you which standard(SAE) socket to use with your metric(mm) fasteners, it is not a measurement conversion chart.

Tip: If your slightly over-sized socket doesn't fit you can try placing a thin piece of cloth over the bolt before pressing the socket into place. The thin cloth will fill the small amount of extra space and allow the socket to grip more tightly.

A 33mm metric socket is 1.29921 inches in size which most closely matches a 1 5/16 standard size socket. A 1 5/16 standard size socket is 33.34mm which is a little bit bigger than a 33mm socket but it is the standard size socket that best fits over a 33mm bolt.

Unless the 33mm nut or bolt that you need to remove is rounded a 1 5/16th socket will work. Care should be taken not to strip the bolt, the small amount of wiggle room is sometimes enough to cause a bolt to strip. Before using a grinder or torch to loosen a stripped or rounded bolt try padding the socket with a light cloth, it often works!

Standard Socket vs Metric Socket Sizes

Standard sockets are measured in inches while metric sockets are measured in millimeters(mm). Depending on the region you live in, one measurement system will be more common than the other. This can become frustrating because different manufacturers also embrace different measurement systems.

Most sockets don't quite fit over bolts of the opposite measurement system so scraped knuckles and rounded bolts are unfortunately common.

Properly organizing your sockets is key

The key to quickly grabbing the right socket when converting between metric and standard sized sockets is to keep your sockets neatly organized. Place your standard sized sockets in your toolbox from smallest to largest and place your metric sockets directly beside them.

Now if your standard socket is slightly too big and the next smallest socket is too small you'll know to grab the metric socket immediately beside the standard socket for a perfect fit.

If lining up your sockets next to each other isn't possible you can always print a socket size conversion chart and keep it in your toolbox next to your sockets.

- Related size conversion questions. Since we're on the topic of standard vs metric socket sizes here are answers to more common conversion questions

What is a 36 mm socket in standard size?

A 36mm socket is 1 7/16" in standard(SAE) size, almost. 1 7/16" converts into 36.5125mm so a 1 7/16 socket is the standard socket that best fits a 36mm fastener.

What is a 30 mm socket in standard size?

A 30mm socket is 1 1/4" in standard(SAE) size, almost. 1 1/4" converts into 31.75mm so 1 1/4 is the closest standard socket that may fit your 30mm fastener.

What is a 22mm socket in standard size?

A 22mm socket is 7/8" in standard(SAE) size, almost. 7/8" converts into 22.225mm so 7/8 is the closest standard socket that may fit your 22mm fastener.

What is a 17mm socket in inches?

A 17mm socket is 11/16" in standard(SAE) size, almost. 11/16" converts into 17.4625mm so 11/16 is the closest standard socket that may fit your 17mm fastener. standard(SAE) sockets are measured in inches.

What is a 13mm socket in SAE?

A 13mm socket is 9/16" in standard(SAE) size, almost. 9/16" converts into 14.2875mm so 9/16 is the closest standard socket that may fit your 13mm fastener. note: If your 13mm fastener is slightly worn or you don't have a 9/16" socket you may find that a 1/2" (12.7mm) socket works.

I hope you found this mm to standard size socket conversion chart helpful. If you need to convert Standard(SAE) sockets to Metric(mm) sockets there is a great conversion chart on Socket Size.

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