An apparatus for sealing a passage through tissue includes a tubular member, a plug, and a locator member. The plug is disposed on a distal end of the tubular member and includes an external thread. The locator member is inserted into a lumen of the tubular member until a distal portion is disposed beyond the plug. The distal portion includes a helically wound wire and a tether coupled to the wire that is movable for causing the wire to buckle. To seal a passage communicating with a blood vessel, the distal portion of the locator member is inserted into the passage, and the plug is threaded into the passage until the distal portion extends into the vessel. The tether is pulled to buckle the wire, and the plug is unthreaded until the buckled wire contacts a wall of the vessel, whereupon the plug is released to seal the passage.