A toggle-bolt-like blind-end connector fastens sheet-metal panels to fiber-board ducts by passing through pre-bored holes in the metal panel and punching its own hole in the fiber-board by a sharply pointed conical head mounted on a barbed-ring shaft. An expandable spider is fixed at the base of the head and is held collapsed against the shaft by a short sleeve. The sleeve has an end flange to limit its following the head and spider through the hole punched in the fiber-board, thus allowing the spider to expand inside the duct, after which expansion the shaft is pulled outwardly to press the expanded spider against the inner surface of the fiber-board. Next a resilient-material nut having shaft-gripping barbed-rings in its bore is pushed onto the exposed end of the shaft to engage the sheet-metal panel. The barbed-rings on the shaft facilitate breaking-off the unneeded end of the shaft.