Abstract: A fastener, intended for fastening a sandwich panel (b) to a support (a), and including a headed bolt (1) having a break off tail portion, and a flanged tubular body (4) into which the main portion of the shank (3) of the bolt is pulled so as to lockingly interengage the body and set the fastener, includes a deformable tubular spacer (10) disposed on the shank (3) of the bolt (1) between the body (4) and the head (2) of the bolt (1). The spacer (10) is in the form of a sleeve having a tubular central core, and peripheral grooves (12) between which are annular fins (11). The spacer is capable of being deformed to a substantially shorter axial length by axial compression under substantially constant predetermined load.