in s direction at 200 t m the core obtained was about 19 in elongation at break the core 2 39 was then sheathed with a covering layer which was formed in the same manner as in embodiment 1 by plaiting twelve silk strands into a braid at a density of 29 stitches cm whereby a suture of usp4 0 in size was obtained the covering layer was about 19 in elongation at break the suture thus obtained and having a small size also exhibited excellent characteristics like the suture of embodiment 1 sutures of varying sizes were prepared in the same manner as above and tested in comparison with conventional sutures the results are shown in table 1 in which the sutures of usp1 0 and usp4 0 in size were made of materials different from those of embodiments 1 and 2 accordingly these sutures were slightly different from the above sutures in the results achieved table 1__________________________________________________________________________usp size 2 1 1 0 2 0 3 0 4 0 5 0 6 0__________________________________________________________________________inventionnumber of component 16 16 16 16 12 12 8 6strands of covering layercore ratio 47 33 33 33 20 20 11 14elongation of break 27 8 25 0 23 7 22 2 20 3 20 0 19 4 18 5breaking strength kgf 6 05 3 88 2 92 2 27 1 48 0 95 0 58 0 30flexibility cm 18 5 17 5 17 0 17 0 16 0 15 5 12.