Firearm accessories; Firearm interface attachment system; Firearm rail mounting system; Firearm components; Component parts for firearms and guns; Firearm attachments, namely, modular external rail systems for firearms; Firearm attachments, namely, external modular rail systems for attaching accessories to firearms; Firearm attachments, namely, mounts for attaching accessories to a firearm; Firearm attachments, namely, mounts for attaching ancillary equipment to a firearm; Firearm attachments, namely, adapter plates for attaching accessories to a firearm