Abstract: A dilator includes a shaft with a tapered portion having an outer diameter that is smaller at a distal end than at a proximal end; a proximal end portion provided at a proximal end side of the tapered portion; and optionally a distal end portion provided at a distal end side of the tapered portion. Pitches of adjacent portions of the spirally-arranged protruding portion provided on the tapered portion are different (either smaller or larger) than those of adjacent portions of the spirally-arranged protruding portion provided on distal end side of the proximal end portion and/or on the distal end portion.

Abstract: A dilator includes a hollow shaft having a tapered portion and a body portion having a distal end located at a proximal end of the tapered portion. The tapered portion has an outer diameter that is smaller at a distal end than at a proximal end, and the body portion extends toward a proximal end side in an axis direction of the shaft. A spirally-arranged protruding portion is provided on an outer peripheral surface of the tapered portion, and the spirally-arranged protruding portion has gaps between adjacent portions of the spirally-arranged protruding portion along an axis direction of the shaft. A proximal end of the spirally-arranged protruding portion is located at the proximal end of the tapered portion.

Abstract: A dilator includes a shaft with a tapered portion having an outer diameter that is smaller at a distal end than at a proximal end; a proximal end portion provided at a proximal end side of the tapered portion; and optionally a distal end portion provided at a distal end side of the tapered portion. Pitches of adjacent portions of the spirally-arranged protruding portion provided on the tapered portion are different (either smaller or larger) than those of adjacent portions of the spirally-arranged protruding portion provided on distal end side of the proximal end portion and/or on the distal end portion.

Abstract: A dilator includes a hollow shaft having an outer diameter that is smaller at a distal end than at a proximal end, and a connector connected to the proximal end of the shaft. A spirally-arranged protruding portion protruding outwardly is provided on an outer peripheral surface of the shaft. The spirally-arranged protruding portion has gaps between adjacent portions of the spirally-arranged protruding portion along a longitudinal axis of the shaft. The shaft has a first position and a second position along the longitudinal axis, the second position being located distal to the first position. The outer diameter of the shaft is smaller at the second position than at the first position. An inclination angle of the spirally-arranged protruding portion relative to the longitudinal axis is different at the second position than at the first position.