For an arc radius [i]r[sub]1[/sub][/i] centred at the origin and an arc radius [i]r[sub]2[/sub][/i] centred at [i](x, 0)[/i], a suitable fillet by this method has:[br][list][*]radius [math]r_3=x-r_1[/math][/*][*]centre at the polar coordinates [math]\left[x,2\cdot \arcsin\left(\frac{r_2+x-r_1}{2\cdot x}\right)\right][/math][/*][/list]A physical application is this 3D model for making a [url=https://www.thingiverse.com/thing:2984586]Parametric Assistive Pen Grip[/url] in [url=http://www.openscad.org/]OpenSCAD[/url].