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.

Provided is a double-needle lockstitch sewing machine that can easily sew a fabric rolled into a tubular shape by two rows of lockstitch. The double-needle lockstitch sewing machine includes: a pair of needles (9) that reciprocates in an up-down direction; a pair of loop catchers (40) that is arranged respectively corresponding to the pair of needles (9) and that catch loops of needle threads formed by the needles (9) by rotating about hook shafts (41) extending in the up-down direction; a lower shaft (20) that is disposed in front of the needles (9) and the loop catchers (40) in the cloth feeding direction and extends in the left-right direction and that rotates in conjunction with a main shaft (10) that drives the needles (9); and connecting shafts (30) that extend in the cloth feeding direction and are connected to the lower shaft (20) and the hook shafts (41) in a power transmittable manner to rotate. The loop catchers (40) are rotationally driven in conjunction with an up and down movement of the needles (9) as a rotational power of the lower shaft (20) is transmitted to the hook shafts (41) via the connecting shafts (30). Thus, it is possible to easily sew a tubular article with two rows of lockstitch seams.

A thread feeding device of a sewing machine includes a needle bar movable vertically to pull an upper thread through a fabric, and movable between left and right terminal positions. An imaginary plane to which the needle bar is normal is defined, and includes left and right boundary lines which pass through the left and right terminal positions. An inner rotary hook includes a thread tensing unit disposed on a hook surrounding wall. A lower thread passes through and abuts against the thread tensing unit to define at least one thread abutting point. A final abutting point where the lower thread passes through the thread tensing unit immediately before reaching the fabric is defined, and is projected on the imaginary plane at a point that is interposed between the boundary lines.

Provided is a double-needle lockstitch sewing machine that can easily sew a fabric rolled into a tubular shape by two rows of lockstitch. The double-needle lockstitch sewing machine includes: a pair of needles (9) that reciprocates in an up-down direction; a pair of loop catchers (40) that is arranged respectively corresponding to the pair of needles (9) and that catch loops of needle threads formed by the needles (9) by rotating about hook shafts (41) extending in the up-down direction; a lower shaft (20) that is disposed in front of the needles (9) and the loop catchers (40) in the cloth feeding direction and extends in the left-right direction and that rotates in conjunction with a main shaft (10) that drives the needles (9); and connecting shafts (30) that extend in the cloth feeding direction and are connected to the lower shaft (20) and the hook shafts (41) in a power transmittable manner to rotate. The loop catchers (40) are rotationally driven in conjunction with an up and down movement of the needles (9) as a rotational power of the lower shaft (20) is transmitted to the hook shafts (41) via the connecting shafts (30). Thus, it is possible to easily sew a tubular article with two rows of lockstitch seams.

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.

A thread feeding system for any machine that requires a locking stitch is provided. The lower thread of the lock stitch is delivered from the inside of a rotary hook system or oscillating system of a lock stitch sewing machine. The rotary hook or oscillating hook is held in place by a bearing which is then attached to the chassis of the sewing machine. The rotary hook or oscillating hook is allowed to be driven by teeth on the inner bearing, and they may be located inside or outside, fore or aft to the positioning of the outer bearing. This allows for the void now left inside the rotary hook or oscillating hook where a pipe or tube is placed to feed the lower locking stitch thread.

Provided is a horizontal rotary hook including: an inner rotary hook including an attracted member made of metal in an outer lower surface portion; a permanent magnet that attracts the inner rotary hook; a magnet plate accommodating the permanent magnet and provided with a mounting hole at a center of a diameter thereof; a non-metallic outer rotary hook accommodating the magnet plate and having a shaft hole at a center of a diameter of an inner bottom portion thereof; and a hook supporting shaft that is inserted through the hole of the magnet plate and the shaft hole of the outer rotary hook and includes, at an upper end thereof, a flange for rotatably supporting the outer rotary hook and the magnet plate. A friction coefficient of a contact surface of the magnet plate that comes into contact with the outer rotary hook is set to be larger than a friction coefficient of the flange of the hook supporting shaft.