Var 187 or 187-B should work. These freewheel tools are larger than most. They measure around 40 mm in diameter. VAR 188 was smaller in diameter and will NOT fit.
Here are 2 comparison photos showing the 187-B and 188 placed beside each other.
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http://www.flickr.com/
BOB HANSON, ALBUQUERQUE, NEW MEXICO, USA