Patent ID: 8717736

Claim:
A lightning protection fastener comprising: a fastener member for fastening a second member to a first member which constitutes an airframe of an aircraft and the fastener member having a shaft which penetrates the first member and the second member and protrudes on a side of at least one of the first member and the second member; a fastening member mounted on the fastener member shaft which protrudes on the side of at least one of the first member and the second member; a cap made of an insulating material and the cap being mounted so as to cover the fastener member shaft and the fastening member; and a sealant made of an insulating material and filled into the cap to fill any space between the cap and the fastener member and the fastening member, wherein the cap includes an opening adapted to house the fastener member shaft and the fastening member as well as a through-hole formed in a wall surface of the cap, and inside diameter D 1 of the cap on the side of an end portion of the opening which faces the first member or the second member and hole diameter D 2 of the through-hole are configured to satisfy 0.10≦D 2 /D 1 ≦0.27, wherein after installation of the cap, the sealant completely fills the space between the cap and the fastener member and the fastening member, and part of the sealant spills out of the cap through the through-hole.