There's about a half inch of cylindrical part on the wiper arm that is not wide enough to fit over the base of the bolt on the wiper motor. I nicely ground it all off and the wiper arm then could sit all the way over the bolt and so the nut could be put in and tightened. That's all. It fits in snug and well.

The arm is all very hard plastic and works well. Granted the OEM wipers are metal but appear out-dated . I think the new arms + blades have transformed the rear of my X5 and it now looks smashing and different- may be I should christen her X5.5 Next to be upgraded are the front wipers.

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'05 E53 X5 4.4i, '97 E39 528, '07 E92 335i, '16 F86 X6M.