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

use with this bolt - http://www.thingiverse.com/thing:936191

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:

outer_diameter = 14
thickness = 2
nut_thread_outer_diameter = 10.5
head_height = 5
drive_type = socket
nut_resolution = 1.0
type = nut
wing_ratio = 1
non_thread_length = 0
inner_diameter = 8
thread_length = 25
head_type = hex
thread_step = 2
texture = exclude
nut_type = normal
nut_step_shape_degrees = 45
drive_diameter = 5
nut_height = 5
nut_thread_step = 2
thread_outer_diameter = 8
facets = 6
countersink = 2
slot_depth = 2
nut_diameter = 14
step_shape_degrees = 45
non_thread_diameter = 0
slot_width = 1
head_diameter = 12
resolution = 0.5