Some of us use nylon monofilament thread for rigging. One of the neat features is that you can apply heat to it after it is fastened in place, and it will shrink and become more taut.
The problem has been how to heat it. Some folks use a blown-out match, some a heated knife blade. I used a soldering iron. But distance was critical. Too close and you melt or break the thread, too far and nothing happens.
The latest Fine Scale Modeler has a tip about using an "embossing gun" to heat styrene before bending. This sounded like it might be useful for heating rigging thread. I went to my local Michael's craft store and found one. It sells for twenty five bucks, but I had one of their frequent discount coupons so it cost me about half that.
It works well. It is smaller than a blow dryer, and the air velocity is considerably less. Still pretty hot air, but I have not broken any rigging threads yet. Don't know why they call it a "gun" because it is not gun-shaped- it is a straight tube.