The X2C040000B91HA-Z is an SMD Crystal Resonator manufactured by Harmony. It has a frequency of 40MHz ±10ppm and comes in a compact SMD-2016 package. The part is RoHS compliant, meaning it is free from hazardous materials such as lead, mercury, and other harmful substances defined by the Restrictions of Hazardous Substances Directive. It is primarily used as an oscillator in circuits requiring precise timing, such as computers, radios, and amplifiers.