specialized nozzles for two-part adhesives (epoxy, polyurethane) that efficiently blend components with internal square/quadro elements for strong, consistent bonds, crucial for industries like automotive repair or construction; they attach to cartridges (often 45ml, 1:1/2:1) via bayonet or threaded fittings, ensuring precise, low-waste application and are available in bulk from suppliers like 3M or generic brands on sites like eBay and Alibaba.