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Re you question:

I don't have that include library, so just used a cylinder) instead.

include <MCAD\polyScrewThread_r1.scad>
//screw_thread(15,4,55,10,PI/2,2);

difference() {
translate ([-10,-10,10])
cube ([20,20,100]);
cylinder(r=5,h=111); // made sure it was longer than cube

}

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ie put the screw_thread() where the cylinder() is.

Unless specifically shown otherwise above, my contribution is in the Public Domain; To the extent possible under law, I have waived all copyright and related or neighbouring rights to this work. This work is published globally via the internet. :) Inclusion of works of previous authors is not included in the above.

The TPP is no simple “trade agreement.”  Fight it! http://www.ourfairdeal.org/

View this message in context: http://forum.openscad.org/How-to-combine-difference-and-include-tp12371p12388.html
Sent from the OpenSCAD mailing list archive at Nabble.com.