Measure the area to be covered with trim, using the cloth tape measure for accuracy.
Lay the chair down, if possible, so gravity can assist you as you lay out the nailhead trim. Trim on a roll needs a nail only every third space, using false nailheads in between.
Start in a corner. Draw the fabric taut over the batting and line up the trim on the edge of the fabric. Using a mallet or tackhammer, gently nail the first nail into the hole.
Continue around the chair back or arm, bending the trim as necessary.
Cut the trim with wire cutters at the corners. If you can't end the line of trim at a nailhead, cut the trim at the closest hole and add individual nails to finish off the line. Use a nail spacer to maintain consistency between the nailheads. Start the next row by cutting off the two false nailheads so you can start the new row with a nail.