Check the listing for details. Humidity Indicator/"Eyeball" for SCUBA Compressor or Fill Panel. Condition: New. Listed at 10.82 USD. TFM Engineering carries a variety of extremely useful valves for SCUBA compressor and high pressure breathing air applications (all are 1/4" NPT). They are anodised aluminium and are very light - but all are 400bar rated unless otherwise specified. Brass versions are often available by special order, as are other special valves, high pressure regulators, etc. Only one shipping fee is required for multiple valves. 40-305 Moisture & CO indicator ("Eyeball") – a disc/element (not included) inside changes colour in the presence of moisture or carbon monoxide allowing you to get a better idea of your air quality than just smelling it, and much earlier warning it is time to change the filter. 40-306 Humidity Element 20/40/60 40-307 CO/Humidity Element -