Have a look here:

https://www.polymax.co.uk/metric_spanner_sizes

As told 31mm and 33mm aren‘t usual metric spannersizes. This spanners and sockets are the result of the forgotten knowledge of the imperial sizes. If you hab a look in a metric spanner or socketset, there are no 29, 31 or 33 sockets.

This sizes are styled to match imperial nuts. If you‘ve got a nut and the the 30mm and the 32mm wouldn‘t fit, you measure it.
And how? Metric, or when imperial never you measure 1 5/16… With the relativ new technic of flangedrive spanners and sockets,
Doesn‘t matter if the Tool (or the nut) doesn‘t fit 100%.

I think it would be worth to keep the imperial sizes! Not only the fizz in the pint bottle.

Greets René

2018 plus4 (sports green)
with a homemade really shiny red tinted dash…