Nice but Black is not the better way to see, and code is necessary for my use.

Nice library, great thanks JustKrys.

ISOThreadUM2.scad

Removed error in thread_in_ring function (thinknes dont work)

module thread_in_ring(dia,hi,thk)

{

difference()

{

cylinder(r = (dia/2)+thk,h = hi);

translate([0,0,-1]) cylinder(r = (dia/2)+0.1, h = hi+thk);

}

}

And add champfer on thread equal 20% of pitch.

module thread_in_pitch(dia,hi,p,thr=$fn)

// make an inside thread (as used on a nut)

// dia = diameter, 6=M6 etc

// hi = height, 10=make a 10mm long thread

// p=pitch

// thr = thread quality, 10=make a thread with 10 segments per turn

{

h=(cos(30)*p)/8;

Rmin=(dia/2)-(5*h); // as wiki Dmin

s=360/thr; // length of segment in degrees

t1=(hi-p)/p; // number of full turns

r=t1%1.0; // length remaining (not full turn)

t=t1-r; // integer number of turns

n=r/(p/thr); // number of segments for remainder

difference(){
for(tn=[0:t-1])
translate([0,0,tn*p]) th_in_turn(dia,p,thr);
for(sg=[0:n])
th_in_pt(Rmin+0.1,p,s,sg+(t*thr),thr,h,p/thr);
cylinder ( d=dia-p*0.8, h=hi);
} // make champfer on thread = 0.8*thread pitch // Anton Belov 18.05.2017

}

and make champfer on nut bottom

difference()

{

union() {

thread_in_ring(30,6,3); // make a ring to enclose an M8 x 10 ISO thread with thickness 2 mm

thread_in_pitch(30,6,1.5); // make an M8 x 10 thread with 1mm pitch

}

cylinder ( d1=33, d2=28.5,h=3); // make champfer on nut

}

Small note: For ABS (and maybe PLA too), scale nuts up by about 2% else they are quite tight.