Patent ID: 7182123

Claim:
A rib comprising a typical upper hole ( 1 . 1 ), a typical lower hole ( 1 . 2 ) and a typical joining profile ( 2 ), as well as a first ( 3 ) and a second ( 4 ) internal folding, a third intermediate ( 5 ) and a fourth external folding ( 6 ), ending in a fifth reversed folding ( 7 ), characterised in that the fourth external folding ( 6 ) and the fifth reversed folding ( 7 ) extend on both opposite vertical sides of the rib, to the lower part of the rib where they end with two chamfers ( 8 ) on each opposite lower corner of the rib, and the third intermediate folding ( 5 ), the fourth external folding ( 6 ) and the fifth reversed folding ( 7 ) extend on the upper part of the rib to connect two vertical walls of the rib and form two chamfers ( 9 ) located on both opposite upper corners of the rib, wherein centrally in relation to the upper hole ( 1 . 1 ), on its both sides, and above, on the surfaces of the second internal folding ( 4 ) and the third intermediate folding ( 5 ) there are three spherical concavities ( 10 ), and on both sides of the lower hole ( 1 . 2 ) there are two similar spherical concavities ( 11 ).