The improved installation tool for installing grommets in a hole in a panel having a countersink end includes an anvil having a convex surface for contacting the head of the grommet after the grommet is installed in the hole. A flaring die having a tapered tubular portion for inserting into the grommet is mounted on the open end there in and chamfered surface for deforming the end of the grommet so that it is deformed into the countersink. This is accomplished by a threaded rod that extends through a hole in the anvil, grommet and threadably engages internal threads in the die. Withdrawing of the rod causes the die to be moved against the grommet and flares the end of the grommet into the countersink and locks it in place.