For a givenprotractor angle
ring inside diameter
ring width
engraving tool shank diameter
θ
D
w
d

}
degrees

inches or millimeters

this calculator will determine the fourth value if you enter any three.

w= d=
θ=° D=

θ = sin-1 d  + tan-1 w
4D2w2 D
w =  2·D·sinθ - d
2·cosθ
d = 2·D·sinθ - 2·w·cosθ
D =  w  +  d
tanθ 2·sinθ