Method for sewing threads, in which individual folded printed sheets are placed successively in a manner in which they lie flat against one another and are stitched to form a book block by means of at least one stitching needle and by means of at least one hook needle, wherein • the at least one stitching needle introduces a binding thread from the outside, through the fold of a printed sheet to be stitched, inwards between the limbs (8, 9) of said printed sheet, in the process creating a first, single-strand seam on an outer side of the fold, • the binding thread is stored between the limbs (8, 9) of the folded printed sheet and, proceeding from the stitching needle, is transported in the form of a thread loop far enough in the direction of a path of movement of the hook needle that a closed end of the thread loop extends beyond this path of movement, • the at least one hook needle dips into the previously formed thread loop, through a lug of the same binding thread that has been produced on the outer side of the fold during the stitching of the preceding printed sheet and through the fold of the printed sheet to be stitched, inwards between the limbs (8, 9) of said printed sheet, captures said thread loop during a return stroke travel, conveys said thread loop from the inside outwards, through the fold of the printed sheet to be stitched and through the lug located on the outer side of the fold, and in the process creates a second, double-strand seam, which is spaced apart from the first, single-strand seam, on the outer side of the fold, • the hook needle has a recess on one side, which recess forms a hook which serves to receive the binding thread, which hook needle is rotated about its longitudinal axis for the purpose of stitching the printed sheet and in the process the hook is positioned in different rotary positions, • before the penetration from the inside outwards of the fold of the printed sheet to be stitched and of the lug of the previously stitched printed sheet, the hook needle is rotated about its longitudinal axis in such a way that its hook is positioned in a vertical plane of symmetry of said lug and on a side of the hook needle that faces the previously stitched printed sheet, characterized in that, before the capturing of the thread loop, the at least one hook needle is rotated about its longitudinal axis in such a way that the hook of said hook needle is positioned, on its side which is opposite the stitching needle and at an angle of +/- 85°, preferably at an angle of +/- 50° and particularly preferably at an angle of +/- 15° with respect to a first vertical plane through the fold of the printed sheet to be sewn. • the at least one stitching needle introduces a binding thread from the outside, through the fold of a printed sheet to be stitched, inwards between the limbs (8, 9) of said printed sheet, in the process creating a first, single-strand seam on an outer side of the fold, • the binding thread is stored between the limbs (8, 9) of the folded printed sheet and, proceeding from the stitching needle, is transported in the form of a thread loop far enough in the direction of a path of movement of the hook needle that a closed end of the thread loop extends beyond this path of movement, • the at least one hook needle dips into the previously formed thread loop, through a lug of the same binding thread that has been produced on the outer side of the fold during the stitching of the preceding printed sheet and through the fold of the printed sheet to be stitched, inwards between the limbs (8, 9) of said printed sheet, captures said thread loop during a return stroke travel, conveys said thread loop from the inside outwards, through the fold of the printed sheet to be stitched and through the lug located on the outer side of the fold, and in the process creates a second, double-strand seam, which is spaced apart from the first, single-strand seam, on the outer side of the fold, • the hook needle has a recess on one side, which recess forms a hook which serves to receive the binding thread, which hook needle is rotated about its longitudinal axis for the purpose of stitching the printed sheet and in the process the hook is positioned in different rotary positions, • before the penetration from the inside outwards of the fold of the printed sheet to be stitched and of the lug of the previously stitched printed sheet, the hook needle is rotated about its longitudinal axis in such a way that its hook is positioned in a vertical plane of symmetry of said lug and on a side of the hook needle that faces the previously stitched printed sheet,