assuming that you are working with a 12 inch length requirement you might consider the Rockwood 556WS-626 Windstorm Lever Extension Flush Bolt - Satin Chrome Plated Brass as seen here:
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This product is rated for use in windstorm rated products where you will have quite excessive positive and negative pressure that would be created in a hurricane or tornado environment and because this flush bolt has a solid rod rather than a piece of threaded rod that is connecting the unit together does indeed make this a more heavy-duty option and in fact I will sell this windstorm rated flush bolt in all instances where I know that I have a pair of doors when the active door and the inactive door especially will receive a high volume of use.
The link above is to a satin chrome finish but reach out to our sales department where we can take an order from you for that same product in a black powder coat.