~ Ball and Kerr 2-piece mason jars lids have an outside diameter of 2 3/4". ~ HyLids hygrometer lids allow you to monitor the humidity inside a jar and make any adjustments you may need. ~ Great for storing partially dried herbs at their peak for a prolonged period of time. ~ Available in Regular and Wide Mouth sizes with either an Analog or Digital hygrometer. ~ Calibration and adjustment instructions included.