Rad and bounding box work a bit differently -
rad returns size along object x, y, z (result doesn't change when obj rotates)
bounding box returns size along scene axis (result changes when obj rotates)
here top is the parent null containing 3 objects
import c4d
from c4d import utils
def main():
global x, y, z
mg = top.GetMg()
result = utils.GetBBox(top, mg)
# returns 2 vector tuple >> center position and radius of bounding box
radius = result[1]
x = radius.x * 2.0
y = radius.y * 2.0
z = radius.z * 2.0
bounding box 3 objects.c4d
Bounding Box position can sometimes give the 'wrong' result.