the basket 6 complete with slide 15 for the axial constraint of the bobbin case 8 to the basket to prevent accidental disassembly during the sewing operation and complete with lever 16 that with its leverage system created on slide 15 allows the operator to disengage the slide 15 and herewith the bobbin case 8 from the axial constraint to the basket 6 to allow the removal of the bobbin case and complete with tension spring 9 to give tension to the bobbin thread whose graphical representation is omitted wound on the bobbin 4 housed inside the bobbin case 8 a bobbin 4 on which is wound the bobbin thread not shown is housed in the bobbin case 8 and is constrained within the basket 6 by the mounting of the bobbin case 8 on the basket 6 fig3 shows the only sub assemblies basket 6 bobbin 4 and bobbin case 8 of the rotary hook 12 of fig2 known sectioned on a plane passing through the axis of rotation u201c u03b1 u201d there are visible the basket 6 comprising a well 18 of the basket 6 apt to house the bobbin case 8 with inside the bobbin 4 an inner diameter 19 delimiting said well 18 of the basket 6 in which fits the outer diameter 20 of the bobbin.