Customized version of http://www.thingiverse.com/thing:193647

use with this bolt - http://www.thingiverse.com/thing:936436

Works better to print these two at a time. You need to give the model time to cool or eventually the hot end just stirs around molten plastic and you wont get any good thread definition.

Using the following options:

thickness = 2
thread_length = 7.5
resolution = 0.5
nut_type = normal
nut_step_shape_degrees = 45
facets = 6
nut_resolution = 1.0
non_thread_diameter = 0
countersink = 2
thread_outer_diameter = 5.5
head_height = 5
nut_height = 5
step_shape_degrees = 45
non_thread_length = 12.5
texture = exclude
type = nut
outer_diameter = 14
slot_depth = 2
nut_diameter = 10
drive_type = socket
nut_thread_outer_diameter = 6.5
wing_ratio = 1
drive_diameter = 5
head_type = hex
nut_thread_step = 2
thread_step = 2
head_diameter = 10
slot_width = 1
inner_diameter = 8