Metric and Imperial Measurements:

When tools such as spanners and sockets are referred to as being 'metric', it means that they use the SI for measurements. In other words, they are measured in millimetres.

The Imperial equivalent (the old English system) is in fractions of an inch. For example:

  • The Imperial equivalent to a 10mm spanner is 3/8"
  • The imperial equivalent to a 19mm spanner is 3/4"
  • The metric equivalent to a 9/16" spanner is a 14mm.
  • the metric equivalent to a 7/16" spanner is an 11mm.

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