Viewed from profile, drywall J-bead resembles a J-shaped channel; two flat sides -- one short and one long -- surround the bead's bottom edge. Builders use J-bead to cap the end of drywall sheets where the sheets butt against dissimilar building materials, such as metal or masonry, or where the drywall's edge remains exposed, such as surrounding an attic access panel. Builders fasten the bead to underlying framework with fasteners or attach bead to drywall sheets with a spray adhesive.
Hook the tape measure's tang on end of the bead. Extend the tape to the desired length of the cut. Mark the cut line across the bead's long flange with a marker; the long flange is the tall portion of the "J" shape.
Cut along the mark with a pair of snips. Rotate the bead and cut through the bottom edge. Cut through the remaining flange -- the short flange -- to complete the cut. Slip the bead over the drywall sheet's edge to ensure a proper fit. Trim the bead to fit, if necessary.
Spray drywall bead adhesive along the drywall sheet's edge and throughout the bead's center channel. Allow the adhesive to set according to the manufacturer's instructions. Most drywall bead adhesives function like contact cement; you must apply adhesive to both surfaces and wait several minutes before joining the separate components.
Align the bead's channel with the drywall's edge. Position the bead's short flange facing away from the wall; the short flange, called the "reveal," is usually exposed and the long flange concealed. Align the ends of the bead with the ends of the drywall sheet's edge.
Slip one end of the bead over the drywall. Press the center portion of the bead over the drywall and slide the remaining end of the bead onto the drywall. Press the bead over the drywall's edge until the interior face of the bead's channel butts against the drywall's edge.
Draw a tape measure along the bead's long flange, mark the cut line with a marker and cut the bead with snips. Fit the bead onto the drywall to check for accuracy and trim the bead's length with snips, if necessary.
Position the bead's short flange facing toward the room's interior. Slip the bead over the drywall's edge. Align the ends of the bead with the ends of the drywall. Press the bead onto the drywall until the interior face of the bead's channel butts against the drywall's edge.
Hoist the drywall sheet into its installation location. While holding the sheet in position, drive staples into the exposed flange. Staple the bead at each end and every 10 to 12 inches across the bead's center.