These 29 mm heavy-duty filter discs are designed to cover a 3/8" gas exchange hole on custom-made spawn lids. We had this size disc manufactured to our specifications due to overwhelming demand for a small pre-cut filter disc for the production of custom spawn jar lids. They are designed to be secured over gas exchange holes in spawn lids with a heat-resistant sealant like RTV silicone. These discs are 29 mm in diameter, a little bigger than a US quarter coin but smaller than a US half dollar coin. They are designed to cover a gas exchange hole drilled with a 3/8" forstner drill bit. They allow for gas exchange while providing 99.97% efficiency filtration down to 0.3 microns. Autoclavable. They are 100% reusable and the best filter available for spawn production or canning jar cultivation.
These discs are superior to hand-cut discs because manually hand-cutting synthetic filter discs into small circles tears the synthetic fibers of the disc and results in an increase in pore size of the disc (making it ineffective against contaminants). These discs have been professionally manufactured to the perfect size for custom spawn jar lids.
To use this filter, secure it over the 3/8" gas exchange hole on top of your custom-made spawn lid with RTV silicone.