I need new wiper blades so today went to Wilco Motosave and gave them my registration expecting them to know exactly what wipers I need but their system came up with two different sized pairs.

Does anyone know why there wouldn't just be a standard pair size..?

I can measure the current ones and get a size to match but just wondered why there isn't one recommended pair.

Apparently Wilco don't stock Bosch anymore because Bosch just upped their prices massively but that's whose wipers I usually use so will source elsewhere when I can get definitive size/ref. 

Might be different sizes for RHD/LHD. Just a guess though.