Torus

Hole Radius of a torus formula
$R_h \;=\; R - r$
Symbol	English	Metric
$R_h$ = radius of the hole	$in$	$mm$
$r$ = radius of sphere	$in$	$mm$
$R$ = radius of center of sphere	$in$	$mm$

Surface Area of a torus formula
$S \;=\; 4 \cdot \pi^2 \cdot R \cdot r$
Symbol	English	Metric
$S$ = surface area	$in^2$	$mm^2$
$\pi$ = Pi	$3.141 592 653 ...$	$3.141 592 653 ...$
$r$ = radius of sphere	$in$	$mm$
$R$ = radius of center of sphere	$in$	$mm$