40MM NATO Gas Mask Thread to 3M™ Bayonet Adapter

This 40 mm NATO thread to bayonet adapter allows the user to clock filter cartridges for better ergonomics, to prevent obstructed views, or based on user preference. This is unique feature from other available threaded 40 mm adapters that direct thread on, requiring the use of shim or washers to change the clock position of filter cartridges, and do not allow the bayonet to be clocked at different positions easily. The two piece design consist of a threaded outer shell that clamps down on the inner bayonet adapter that can be clocked independently. The adapter bayonet chosen was 3M, due to wider and more commonly availability of filter cartridges from different industry use, and would enable greater cross compatibility of filter cartridges to full face 40 mm NATO CBRN masks.

This adapter was designed to help support the recent PPE shortage faced across the world. Unfortunately, many manufactures are currently reallocating and asking dealers to restrict the sale of respirator filters, respirators and accessories to the general public. Coupled with this shortage, hospital administrators have instructed front line clinicians to source their own PPE. With the lack of nominal protection from either surgical masks, and N95s, front line health care providers, 1st responders, and critical infrastructure staff have been struggling to find alternatives. Some have been turning to the availability of CBRN full face respirators as a viable solution for not just biological contaminants.. In countries like Sweden, wartime protective masks have just recently been issued to emergency personnel and hospital staff. And other countries may follow this example, as MOPP gear is plenty in many armed forces today. However, 40 mm NATO filter cartridges are more expensive and harder to source for private individuals than commonly available 3M, Scott, MSA, and Honeywell filters. And creating an adapter to fit other manufacturers filter cartridges would help to mitigate PPE shortages.

Disclaimers/Risks:

1.) Requires the 3M™ 6895 Replacement Inhalation Port Gasket, or similar gasket/o-ring, below bayonet to ensure proper seal between cartridge and bayonet. Should be compatible with 3M™ Filters 2000 Series, 3M™ Filter 7093, 3M™ Cartridges 6000 Series or 3M™ Dual Airline Systems.

2.) 3D printing materials are not resistant to many solvents, are water soluble, and degrade when exposed to chemicals. 3D printing this adapter is only a temporarily ad-hoc solution against biological threats. Once supply chain returns to normal, users should purchase OEM NIOSH/EN standard approved adapters and respirator accessories.

Credits

Thanks to mfxpyro for sharing the NATO RD40x1/7 gas mask threads specifications.
https://www.thingiverse.com/thing:3875269/files

And special thanks to FastIndy for local 3D printing support, adventuredepot for initial and continual remote 3D printing support, and Karkovski’s feedback on design.

Dev. Notes:

03/28/2020 – Initial release of model.

03/29/2020 – Resolved fitment issue with 3M™ bayonet, reduced diameter, and added additional clearance to ensure fitment for gasket. Reduced model complexity for fidelity of 3D printers: (1) removed recessed cutout for gasket to simplify 3D printing without ad hoc support, and (2) removed bottom inner shell ring protrusion for additional positive seal as smaller feature geometry may not print properly.

04/01/2020 – Changed outer shell and inner shell ODs to be backwards compatible with comparable 3M™ 701 OEM product. Also increased OAL of bayonet clearance for gasket, after feed back from 3D printing community to ensure proper cartridge fitment. [Gen 3 – Higher Tolerance Model for 3D Printers Properly Calibrated/Scaled]

04/03/2020 – Increased diameter tolerance between outer and inner parts to 1 mm, previously 0.5 mm. And reduced bayonet protrusion OD to ensure better fitment to 3M cartrdiges per Karkoski’s input. [Gen 4 – Looser Tolerance More Universal Fit, Forgiving for Printing Tolerances]