In an earlier video it was explained that the end of the chain stay yoke is located a distance F from the center of the BB shell.
An exception to that rule is when the yoke comes premachined in which case F should be set to zero.
The Cobra Sidewinder version 16 yoke comes premachined for a 1.5" BB shell. So setting F to zero and choosing a 1.5" BB shell will give us the fit we want.
The Cobra Sidewinder version 17 yoke comes premachined for a 2" BB shell. So again, we'll leave F set to zero there.
The Cobra Sidewinder version 18 is not machined and therefore we will set F close to but not quite equal to the radius of the BB shell. Using this unmachined yoke allows us to offset the chain stay by some value E and machine the yoke ourselves to suit that particular interface.