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 (24, 24') positioned within the cap member; the continuous wall member (24, 24') defines an opening providing access to the interior space; the continuous wall member (24, 24') is shaped and sized such that the continuous wall member (24, 24') 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 (24, 24'); wherein a thickness of the continuous wall member (24, 24') between contact locations (34, 36, 38) where the continuous wall member (24, 24') is in contact with the end portion of the fastener is greater than a thickness of the continuous wall member (24, 24') at the contact locations (34, 36, 38); the continuous wall member (24, 24') 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 (24, 24') has a first end surface that is positioned within a first plane; the sidewall forms a wall member positioned spaced radially outward from the continuous wall member (24, 24'), 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, wherein the first plane and the second plane 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 (24, 24') positioned within the cap member; the continuous wall member (24, 24') defines an opening providing access to the interior space; the continuous wall member (24, 24') is shaped and sized such that the continuous wall member (24, 24') 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 (24, 24'); wherein a thickness of the continuous wall member (24, 24') between contact locations (34, 36, 38) where the continuous wall member (24, 24') is in contact with the end portion of the fastener is greater than a thickness of the continuous wall member (24, 24') at the contact locations (34, 36, 38); the continuous wall member (24, 24') 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 (24, 24') has a first end surface that is positioned within a first plane; the sidewall forms a wall member positioned spaced radially outward from the continuous wall member (24, 24'), 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, wherein the first plane and the second plane 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.