Customized version of http://www.thingiverse.com/thing:1157042

Created with Customizer! http://www.thingiverse.com/apps/customizer/run?thing_id=1157042

Using the following options:

treadDepth = 1
treadODBase = 3.5
treadNum = 40
Wheel_Diameter = 50
Wheel_Width = 10
Polygon_Count = 64
treadRotate = 45
treadNumSides = 4
Num_holes = 4
offsetTreadRing = 0
treadODTop = 1
chamferWidth = 0
treadRows = 11