Does anyone know the dimensions of the set screw that holds the pin and spring in that captures the rear take down pin on the MATEN?

I managed to lose mine in the abyss of my garage when trying to remove my take down pin. It appears people do mods to regular AR-15 rear take down pin retainers with 4-40 1/8" set screws, but wasn't sure if that's what Mega used. I'm going to see if Tru-Valu has some set screws, but I'm not terribly hopeful.