It's a break-away mirror - it has two little tabs, one on each side, that snap it into the bracket. Push it forward and it will pop loose, then you can tighten the bracket that it mounts to.

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Houston, Texas
1984 300CD 235K miles, Elvira, one owner
1987 300TD 180K miles
1974 TR6 78K miles Sarah Jane, one owner
OBK #27