RD40 ->2x DAR Ambu filter adapter. Tested. Gas mask NATO

thingiverse

Make sure seam position is random, especially with multiple instances. Optimized for 0.6 nozzle (2 perimeters for 0.6 nozzle, 3 for 0.4 nozzle). PETG. Layer 0.2. No supports. Minor cleanup may be needed, depends on print quality. T connector outer pipe edge, that goes into the threaded adapter, needs to be sanded, or you can play with elephant foot compensation in slicer. Top surface of threaded part must be sanded flat, because it will create seal with mask gasket (sanded areas on last photo) Assembly: Screw in adapter in place, then insert T connector in correct position (it has 7 degree skew). Designed to be used with teflon tape (5-8 winds on biggest pipe,2-5 on filters) or to be glued in, otherwise 3d prints are not airtight, and can leak false air. Use at your own risk.