As with all Oasis humidifiers, you can count on the Oasis 3/4 size Double Bass Humidifier to protect your instrument from cracking in dry winter weather by providing it with the humidification it needs without leaking or hurting your instrument. Using special water absorbing crystals, Oasis Humidifiers keep water in a gelled state to dramatically reduce the risk of water leakage. This product recommends using distilled water as tap or bottled water will clog up it's unique fabric and prevent the proper release of water. To accommodate the large air capacity of the double bass, two humidifiers are generally required to supply sufficient humidity. Due to the high humidity output of this humidifier, the unit should be refilled every three days. The humidifiers fit inside the double bass through the hole at the bottom of the F hole. This humidifier will not fit every double bass. The opening must be 1 ¼” or larger, so it isn’t suitable for half-size or smaller double basses but fits most three-quarter size double basses. The humidifier is suspended by an elastic cord that slips over the neck of the humidifier and is held in place by both tension and the humidifier cap. The cord is knotted at the end and extends through two pieces of felt (user-installed.) One piece of felt is round and fits in the F hole. The other is rectangular and fits outside the double bass keeping the humidifier from falling into the instrument.