| 摘要 |
PROBLEM TO BE SOLVED: To simplify the assembling work for a spiral stairway 30, enabling one worker to hold a tread 25 to lock it to a pole 30 and to fasten bolts 32, 33. SOLUTION: Threaded holes 31, 31 are previously formed in a pole 30 forming the center of the spiral stairway (a). The bolt 33 is loosely screwed into the lower threaded hole 31 (b). A through-hole 8 is formed in the upper part of a fixed plate 6 on the base end side of the tread 25, and a locking cutout 11 with an opening 12 facing downward is formed at the lower part of the fixed plate 6 (b). When the locking cutout 11 of the tread 25 is locked to the bolt 33 of the pole 30, the tread 25 is held to the pole 30 in the communicated state of the screw hole 31 and through-hole 8 (c). The bolt 32 is screwed and fastened into the threaded hole 31 from the through-hole 8 side of the tread 25, and the loosely screwed bolt 33 is also screwed and fastened to firmly fix the tread 25 and the pole 30, thus constructing the spiral stairway (d).
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