I can't be sure as I don't have one, but
https://www.freedommotorsaustralia.com. ... 019_v1.pdfon page 7 shows various adapters including an 8mm spacer in a shot with the locking plate showing relative thickness of both quite well.
Art. nr. 503125
Lock plate with bolts and
8 mm spacer
I'm sure someone can pull out the pixel measuring tape, but the plate looks slightly thinner than 8mm. 6mm,maybe 5mm.
Lots of other measurements in there, might make it reproducible with careful photo analysis.
If only there were an international forum of wheelchair drivers where someone might have one to measure...
Then they could also give us opinions of the Dahl unit.
I see it has electric release, redundant manual cable release, and a tertiary emergency release tool built in to the dock. I appreciate the overengineering, but makes a person wonder why it was necessary. Lots of rearward force (sudden vehicle acceleration or rear end crash) that pin might get jammed (doesn't look likely). Please tell us if you have ever needed to resort to the emergency release tool.
Don't get nervous about my speculation if you have one, it looks very solid and the emergency tool is probably just there for emergency workers that may not know where to look for the cable release in the vehicle.