Customized version of http://www.thingiverse.com/thing:16627
Created with Customizer! http://www.thingiverse.com/apps/customizer/run?thing_id=16627

Using the following options:
additional_tooth_depth = 0
profile = 6
retainer = 1
motor_shaft = 15
idler_ht = 1.5
m3_nut_depth = 2.8
nut_shaft_distance = 1.2
m3_dia = 3.2
m3_nut_flats = 5.7
m3_nut_hex = 1
pulley_b_ht = 8
additional_tooth_width = 0.2
retainer_ht = 1.5
no_of_nuts = 6
pulley_b_dia = 30
idler = 1
nut_angle = 60
teeth = 20
pulley_t_ht = 12