sound tu me like yu hav equilateral triangel inside serkel
serkel diam=3.875, so radius=1.9375
polygon (triangel) side leng=3.3558...distans from hole-tu-hole
triangel...all 3 angels=60
draw vertikal line thru serkel senter & put top av triangel at top weer this hit serkel
get 2 identikal rite triangels...30/60/90
from trig funks, yu find:inside serkel radius=(1/2) outside serkel radius
hite av triangels=(inside radius) + (outside radius)
or yuze triangel side leng=2*(outside radius)*(kosine beta)
alfa= apex angel=360/n=360/3=120deg
beta=(180-alfa)/2=30 deg