Metric sized building blocks (commonly 440 x 100 x 215mm) have been
around since metric sizes arrived in the 70s.

What is the application for 'modular sizes' (eg 390 x 100 x 190 - even
390 x 90 x 190)?

eg

http://www.plasmor.co.uk/html/produc...033e7d91fcfcf4

Is a new standard being introduced? Most block manufacturers websites
show this size in addition to the metric ones.

Also, especially, why 90mm? Anything less than 100mm in a wall leaf
is usually frowned on.

I inadvertently bought some grr...grrr...

Anyone know?

TIA for any info