The tools to do what the OP needs are already in openscad. define a circle the size needed, extrude a thin piece tilt it according the the pitch of the thread Use it to make the spiral with code something like this: newbolt(sz,tal) { $fn=360;// smooth finish thoff=-5.95;// arrange to do only adds for final size tszc=sz+tal;// final size for(i=[0:1:359*1.15])// longer 2 start threads { k=i/30+thoff;// do this addition once per loop, much faster rotate([0,0,i])translate([.5*(tszc),0,k]) threadshape58();// 1st start add half the teeth rotate([0,0,i+180])translate([.5*(tszc),0,k]) threadshape58();// 2nd start of thread other half of teeth } }; ---------------------- Substitute your extruded circle for threadshape58 done. No library magic. This is a snippet from the code that made this pix. The whole is about 800 lines, and has at least a 30% clutter. Lots of other parts, including production tools. I actually use this to make the half nuts Cheers, Gene Heskett. -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author, 1940) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis