The inner joints are 108mm diameter. According to the Spidan Catalog.....
26109 Boot kit
Ø1 [mm]: 24;
Ø2 [mm]: 108; H: 124[mm]; Material: RUB/Metal;
addition
+)Cap; BoreØ: 10.4[mm]; Bores No: 6;
PitchCircleØ: 94[mm]
The outer joints are a different size......
26041 Boot kit
Ø1 [mm]: 24;
Ø2 [mm]: 92; H: 83[mm]; Material: RUB
The inner and outer joints are completely different, as are the boot kits.....
Outer Boot : Audi part # 431498203D or 443498203A (ABS)
Inner Boot : Audi part # 443498201B
All the audi part numbers are getting hits on ebay too. Use Spidan or Lobro for OEM quality. Avoid the spurious brands, these parts are too cheap to fit cheap false economy items.....