There was a time when I cringed when I had to replace a threshold. Getting a tight fit on both sides of the jamb was a time-consuming challenge. But replacing the threshold on an exterior door is not a job to put off; a worn threshold compromises the weather seal. Once I started specializing in finish work, especially doors, I had to come up with a system that would get the job done right the first time.
Hardware stores, home centers, and lumberyards stock a variety of wood thresholds. I prefer 3/4-in.-tall thresholds without a rubber insert. In my experience, the rubber insert can’t be adjusted to contact the door and the jamb precisely. Also, it can become clogged with mud, snow, and ice, so I always take the time to install a sweep rather than use a rubber insert for a weather seal.
The key to getting an exact fit on a new threshold is to use a template to transfer the jamb’s contours to the ends of the threshold, where matching contours must be cut. I make my templates from 1/4-in.-thick hardboard ripped to the width of the threshold. I’ve used this system for almost 20 years, and it never has failed me.