of each of the thread holding members 23 and 24 as shown in fig1 or fig3 the thread support walls 33 and 34 each protrude with a constant height in the height direction a direction y that is perpendicular to the upper surface 1 a the bead mounting face 10 a and also extending along the direction y as shown in fig2 the thread support walls 33 and 34 are positioned between the thread holding members 23 and 24 end edges 13 and 14 as viewed in the direction z and the region between the thread support walls 33 and 34 is the bead mounting surface 10 a when multiple vertical threads are held with predetermined gaps in the direction x by the thread holding portions 23 and 24 these vertical threads are supported by the thread support walls 33 and 34 with a predetermined gap from the upper surface 1 a the bead mounting surface 10 a see fig1 as shown in fig5 a plurality of four in the present embodiment thread hanging portions 41 42 43 and 44 and a plurality of leg portions 51 52 53 and 54 are provided on a lower surface 1 b the surface on the side opposite to the bead mounting surface 10 a of the plate member 1 the main plate portion the thread hanging portion 41 is for hooking one end of each of the vertical threads and is provided in the.