Customized version of http://www.thingiverse.com/thing:21112
Created with Customizer! http://www.thingiverse.com/apps/customizer/run?thing_id=21112
Using the following options:
largeflange = 6
holeaccess = Cowling
cowlingheight = 30
largeholes = 32
largesize = 40
$fn = 80
smallholes = 24
smallsize = 30
largeholesize = 3.5
smallflange = 4
wallthickness = 2
smallholesize = 3.5