How to Replace a Threshold

• The ends of the new threshold have to be notched to fit around both door jambs. This creates a "horn" that extends under the casing. First, measure the width of the right-hand casing, then hook the tape on the threshold's back right-hand corner and transfer that measurement to the threshold's back edge.

• Next, measure the width of the jamb and stop, hook the tape on the same corner, and transfer the measurement to the end of the stock. Use a square to draw a perpendicular line from each mark until both lines intersect.