In thread cutting mechanism portions of a lower thread winding device, two groove portions of an inner threading groove portion and an outer threading groove portion are formed on a holder. In the inner threading groove portion, one end portion is opened to one of an intersecting direction intersecting with a radial direction of the holder at an outer peripheral portion of the holder and another end portion is located at an inner side of a small-diameter bobbin in the radial direction. The outer threading groove portion is located at an outer side of the inner threading groove portion in the radial direction of the holder. In the outer threading groove portion, one end portion is communicated with the inner threading groove portion and located at the outer side of a large-diameter bobbin in the radial direction and another end portion is located at the inner side of the large-diameter bobbin in the radial direction.

Hook for lockstitch sewing machine, both of the rotary type and of the Central Bobbin type (CB-shuttle or CB-hook), which includes a bobbin case (508, 708, 808, 908, 1008, 1108, 1208) with an improved slide, composed of multiple components, including a slide body (515a, 615a, 715a, 815a, 915a, 1115a, 1215a) which performs entirely the functions of guiding the slide on the bobbin case and of creation of the leverage with the lever (16, 16b), and at least one secondary component (582, 782, 882, 982, 1182, 1286), fixed to the slide body and apt to perform the function of slide's claw or guide and/or protection of the thread.

In thread cutting mechanism portions of a lower thread winding device, two groove portions of an inner threading groove portion and an outer threading groove portion are formed on a holder. In the inner threading groove portion, one end portion is opened to one of an intersecting direction intersecting with a radial direction of the holder at an outer peripheral portion of the holder and another end portion is located at an inner side of a small-diameter bobbin in the radial direction. The outer threading groove portion is located at an outer side of the inner threading groove portion in the radial direction of the holder. In the outer threading groove portion, one end portion is communicated with the inner threading groove portion and located at the outer side of a large-diameter bobbin in the radial direction and another end portion is located at the inner side of the large-diameter bobbin in the radial direction.

Hook (11, 12, 13, 14) for a lockstitch sewing machine, or parts of the hook such as the support element of the tension spring (in particular the basket or the bobbin case) or the tension spring itself, including a tension spring (80, 90, 100, 110, 120) that includes a bending towards the outside (with respect to the support element on which it is mounted and with respect to the main bending radius of the tension spring) of the tension spring's extremity designed to press on the bobbin thread, so that the pressure point (P) on the bobbin thread is the point of tangency between the bending radius (R) of the bending of the tension spring's extremity and the support element of the tension spring, so as to generate a stable tension of the bobbin thread.