These inserts extend your drone reed-seats, to allow for a lower pitch of your bagpipe.
Do you have reeds that tune too high on your tuning pins? Do you have trouble tuning your drones to your 'B'-flat or 'A' pipe chanter? If so, drone reed extenders are an easy solution! The drone reed extenders basically add a half-inch to the bottom of your drones, thereby flattening the drone column slightly. As you can see from the picture, the extender fits into your drone reed seat. Do you have a double-toning bass problem??? If so, this is also a good potential fix. Most of the time, tuning the first section of your bass drone lower will help your double-toning problem. The extender naturally does that for you, and requires no adjustment of your reed!