A fastener which extends from a structure and a protection seal cap for enclosing an end portion of the fastener , the protection seal cap comprising: a cap member constructed of a thermoplastic or thermoset material and comprising a sidewall that defines an interior space within the cap member , wherein: the sidewall forms a continuous wall member positioned within the cap member ; the continuous wall member defines an opening providing access to the interior space ; the continuous wall member is shaped and sized such that the continuous wall member can be contacted and deformed by an end portion of a fastener and an interference compression fit created between the end portion of the fastener and the continuous wall member ; wherein the fastener is constructed of a harder material than that of a material which constructs the continuous wall member ; wherein a thickness (T1) of the continuous wall member between contact locations where the continuous wall member is in contact with the end portion of the fastener is greater than a thickness (T) of the continuous wall member at the contact locations ; the continuous wall member extends in a direction parallel to a central axis of the cap member and away from the sidewall of the cap member which defines the interior space , and wherein the continuous wall member has a first end surface that is positioned within a first plane (P1); the sidewall forms a wall member positioned spaced radially outward from the continuous wall member , the wall member extends in the direction , and the wall member has a second end surface configured such that the second end surface extends within a second plane (P2), wherein the first plane (P1) and the second plane (P2) are parallel and non-coplanar, and when the cap member is positioned on the structure , the first end surface is separated from a surface of the structure and the second end surface is in contact with the surface of the structure . the sidewall forms a continuous wall member positioned within the cap member ; the continuous wall member defines an opening providing access to the interior space ; the continuous wall member is shaped and sized such that the continuous wall member can be contacted and deformed by an end portion of a fastener and an interference compression fit created between the end portion of the fastener and the continuous wall member ; wherein the fastener is constructed of a harder material than that of a material which constructs the continuous wall member ; wherein a thickness (T1) of the continuous wall member between contact locations where the continuous wall member is in contact with the end portion of the fastener is greater than a thickness (T) of the continuous wall member at the contact locations ; the continuous wall member extends in a direction parallel to a central axis of the cap member and away from the sidewall of the cap member which defines the interior space , and wherein the continuous wall member has a first end surface that is positioned within a first plane (P1); the sidewall forms a wall member positioned spaced radially outward from the continuous wall member , the wall member extends in the direction , and the wall member has a second end surface configured such that the second end surface extends within a second plane (P2), wherein the first plane (P1) and the second plane (P2) are parallel and non-coplanar, and when the cap member is positioned on the structure , the first end surface is separated from a surface of the structure and the second end surface is in contact with the surface of the structure . <EOS>