We apologize for the confusion, however in the very first video that is regarding the assembly, is of the torsion box. We do not included that in any greenBull kit, as we use too sell it individually! However due to high consumption of materials and high cost(both in shipping and for the kit itself) we have removed it from our inventory and no longer sell it.
This video can be skipped, however if you plan on making a DIY torsion box, this video will be helpful in your build!
The torsion box is not needed, as the frame itself will be more than sufficient in keeping the machine from flexing or vibrating.