| 摘要 |
PURPOSE:To maintain the strength of an expander and to prevent overlapping of touching edges of the expander by disposing projections on flat portions of the inner periphery of the expander, and passing a wire through wire passing holes formed on the projections. CONSTITUTION:An expander 6 having flat portions 9 on the inner periphery side is formed in such a manner as to be radially concave and convex and have a wavy pattern extending in the peripheral direction. The flat portions 9 of the expander 6 are provided with projections 14 having holes 13 permitting a wire 12 to pass therethrough, which are projected inward at the central portions of the flat portions 9 positioned in the vicinity of touching edges 8. The expander 6 has butt end portions 7, 7 put together by passing the wire 12 through the wire passing holes 13 of the projections 14, whereby touching edges 8 are adjusted to each other. Accordingly, there causes no situation the butt end portions 7, 7 of the expander 6 overlap each other. |
