Theres a knack to putting them on which doesnt require taking the arms off. You remove the clip from the wiper blade itself, slide said clip onto the arm, then lift the arm as far as it can go, place the clipless wiper under the clip in the arm, push the arm onto the wiper (click), the clip locks back in place on the wiper and then pull the whole lot back into the arm fully and you should hear a satisfactory "click"
2000 D9 Coupé 2.0 SE EW10J4 Scarlet Red - 5 litres of oil gone in 500 miles!!! Time for a new coupe me thinks
There is no need to pull of the arm. Just don't be rough, otherwise you may end up scratching the glass and the like.
From memory, one of the sizes for the Bosch Aerotwin was from a Zafira, using the original arms. Don't quote me on that though - I fink there is a reference guide on the website or in the auto store (Halfords?) etc etc!