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 problems, here is a way you can fix that.

Standard Socket vs Metric Socket Sizes

Standard sockets are measured in inches while metric sockets are measured in milimeters(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.

A 32 mm socket is the same as a 1 1/4 standard socket

Some metric sockets, like the 32mm socket, do match exactly with a standard sized socket so you see why switching between the two systems can be frustrating. Some fit, some don't, and remembering what fits what can be difficult. Tip: Keep your sockets neatly organized from smallest to largest so that you can quickly test fit alternate sizes.

- 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 30 mm socket in standard size?

A 30mm socket is 1 3/16" in standard(SAE) size, almost. 1 3/16" converts into 30.163mm so 1 3/16 is the closest standard socket that may fit your 30mm fastener.

What is a 36 mm in standard size?

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

OK, all these questions might take a while, this socket conversion chart might be more helpful.

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