Measure out the length that you need to cut the trim with the tape measure and mark the length with the permanent marker.
Extend the mark across the face of the trim by aligning the blade of the combination square with the mark you placed on the trim in step one. Ensure that the base of the combination square is resting flat on the bend the trim before you draw the line with the permanent marker. Flip the combination square to mark the other leg of the trim.
Put on your leather gloves and place your hand at one end of the metal trim with your thumb at the trim's corner.
Apply pressure downward with the thumb that you placed on the corner of trim in step one. If you cannot bend the metal with your thumb, skip to step seven.
Align the jaw of the aviation snips with the line you drew across the trim in step two, starting at the raw edge of the trim and cut toward the bend. Keep forward pressure on the snips as you cut across the face of the trim.
Start the cut on the other leg, after you reach the bend of the trim. When you complete the cut, proceed to step ten.
Put on your face shield and attach an abrasive cutting wheel to the clutched grinder.
Lower your face shield and start the grinder by pressing on the trigger. Align the abrasive blade with the line you placed on the face of the trim in step one.
Work the abrasive blade slowly across the line to cut through the metal. Flip the metal to cut the other leg of the metal trim.
Run the file in a diagonal direction across the edge of the trim to remove the bur left from cutting. File the edge until it has a rounded edge and does not grip onto your leather gloves.