Method of installing a nut mounting grommet

A method of securing a nut assembly to a structural wall, by use of a single circular opening in the wall, said nut assembly having a threaded bolt receiving opening and a nut mounting grommet with an integral nut retainer, said method comprising:

• providing a nut mounting grommet which includes a tubular shank having a substantially constant outside diameter and a substantially constant inside diameter, a nut retainer integral with the tubular shank at one end of the tubular shank of said grommet, and a radial shoulder formed where the tubular shank joins the nut retainer;
• forming a cylindrical opening in said wall, to create a grommet receiving opening close in diameter to the outside diameter of the tubular shank of the grommet, said opening having a sidewall;
• inserting said tubular shank of the grommet into the opening and moving the grommet endwise to place the radial shoulder against the wall;
• providing a mandrel of a type having, in series, a small diameter portion, an increasing diameter portion, and a maximum diameter portion;
• positioning a one-piece split sleeve on said small diameter portion of the mandrel;
• inserting the mandrel and split sleeve into the grommet and positioning the increasing diameter and maximum diameter portions of the mandrel on the nut retainer side of the wall;
• holding the split sleeve and grommet in a fixed axial position within said opening while moving the mandrel axially through the split sleeve, thereby moving first the increasing diameter portion and then the maximum diameter portion of the mandrel axially through the split sleeve, thereby expanding the split sleeve radially and imposing a radially outwardly directed force on the tubular shank of the grommet to expand said tubular shank within said opening;
• wherein the mandrel and the split sleeve are so sized that the radial expansion of the split sleeve exerts sufficient radial forces on the tubular shank of the grommet to plastically expand the tubular shank of the grommet and place the sidewall of said opening into tight gripping contact with the outer surface of the tubular shank of the grommet;
• removing the split sleeve from the tubular shank of the grommet after the mandrel has expanded the split sleeve and the tubular shank of the grommet;
• placing the nut into the nut retainer, with the threaded opening of the nut substantially coaxial with the interior of the tubular shank of the grommet;
• and
• securing a nut having a threaded bolt receiving opening within the nut retainer, including holding it against rotation and preventing it from moving out from the nut retainer.