Worn out threads happen. Given those are in the top plate of the mod itself, if that's the problem you can't fix it without replacing the plate, if you can get the part, or recourse to a machine shop. Try getting a 510/510 adapter and fitting that in. If you can get that to grab, you can fit the DH or the Hellboy into the adapter. And in the future, use an adapter anyway, to avoid thread wear on the mod. Just put the adapter in it and leave it there. When the threads wear, get another adapter.