To clear misconceptions.
Kodak Ltd here in the UK made Half Plate cameras before WWII that were almost identical to the US Eastman Kodak 7x5 cameras, and used plate and film holders that had the same outside dimensions. So you can use Kodak 7x5 holder in a Kodak Half Plate camera and vice versa,
After WWII the International Standards for most film/plate holders were based on Kodak holders outside dimensions. So a an 18x24cm Fidelity DDS has the same outside dimensions as a 10x7, a 5x4 the same as a 9x12cm.
When we get to 7x5, then modern Half Plate, and 13x18cm, holders have the same outside dimensions.
But many of us are using older equipment as well, and there were no standards in terms of plate holder fit here in the UK, pre WWII, only a fairly quick standardisation of plate sizes in the 870's.
Ian