Space frame structure is a kind of structure connected by the node of bolt ball, so the bolt ball is the key component of the structure. In GB standard, the bolt ball is made of 45# steel with the diameter of 100mm to 300mm. Normally there are 3-12 holes in the bolt ball and each axial line of the bolt hole is through the center of the ball.
LF ball is with nice roundness and made of round steel rather than square steel(If they are made of square steel, they would have inner cracks). The holes are well treated before painting in order for smooth assembly.