At least 2 UK sellers on eBay have listed Half Plate 6½" x 4¾" DDS often also marked as 12x16.5 cm, as 7x5 (5x7). These holder will not take 7x5 film only Half plate.
Modern Half plate, European 13x18cm and US 7x5 (5x7) DDS Film holders all have the same outside dimensions, so all fit International backs (for the formats). However, they can only be used with their marked film sizes.
At least 2 UK sellers on eBay have listed Half Plate 6½" x 4¾" DDS often also marked as 12x16.5 cm, as 7x5 (5x7). These holder will not take 7x5 film only Half plate.
Modern Half plate, European 13x18cm and US 7x5 (5x7) DDS Film holders all have the same outside dimensions, so all fit International backs (for the formats). However, they can only be used with their marked film sizes.
The difference between these three film sizes has always caused confusion, and the older wooden ones are not even marked as to which size they are for. Holders for 5x4 cameras are also available to take 9,12 cm film, but at least with these the difference is easier to see. I believe holders for quarter plate were also available for 5x4 cameras, but I've never actually seen one.
Thanks for the heads-up. Here in the States, I have had less than knowledgable evilBay sellers list whole-plate stuff- 6.5" x 8.5"- as 8x10. It always pays to ask very specific questions, especially when shipping is expensive or a lot of trouble