Cap and securing structure part using cap

A securing structure part which includes a fastener which passes through a through-hole formed in overlapping multiple structure elements of an aircraft, a collar which is fastened to a tip part of the fastener protruding from a surface of the structure elements, and a cap which is mounted to surround the tip part of the fastener and the collar, and which secures the structure elements using the fastener and the collar,

• wherein the cap is mounted in a non-engaged state with respect to the tip part of the fastener and the collar,
• wherein a filler engaging part is formed on an inner peripheral surface of the cap, and the filler engaging part has a female threaded helical shape which turns about a center axis of the cap, and engages with a filler which fills a space formed between the inner peripheral surface, and the fastener, the collar, and the surface of the structure element and is cured, and
• wherein the female threaded helical shape includes:
• a first helical engagement part which is formed in a region near a cap inner part of the inner peripheral surface in a center axis direction;
• and
• a second helical engagement part which is formed in a region near a cap opening-end part of the inner peripheral surface in the center axis direction, has a greater inner diameter than that of the first helical engagement part, and has a helical direction which is opposite to that of the first helical engagement part.