shaped pins 5 are inserted in the individual bores 3a before the pipes 4 are attached to the frame 3 and supports 6 are provided between the u shaped pins 5 the transverse threads z are then threaded through the u shaped pins 5 and over the blocks 6 one transverse thread z is provided for each row of u shaped pins 5 next the pipes are simultaneously inserted into the respective bores 3a and over the u shaped pins 5 thus the transverse thread z are received by the notches 4a however since the blocks effectively form spaces above the recesses 3 the insertion of the pipes pushes the transverse thread into the spaces consequently the transverse thread z is arranged in a zigzag fashion as shown in fig5 a accordingly the necessary length of the transverse thread z will vary by selecting different thickness of the supports 6 under such conditions the first and second threads x and y and the bias threads b1 and b2 are woven between the gaps of the pipes 4 on the frame 3 so that these threads are looped about the outer surfaces of the pipes 4 provided on the end portion of the frame 3 the x thread layer the y thread layer and the bias thread layers are therefore sequentially woven in the named order the first thread x is arranged to be woven back and forth extending in parallel to the bend 2 of the frame 3 the second thread y is arranged to be woven back and forth in a direction that extend perpendicular to the bend 2 of the.