As other owners have discovered, Kel-Tec did not intend for the rail screws to vibrate loose or come out easily, so they used some sort of Loctite type thread locker and a lot of torque.
For that reason people have stripped the threads.
There's another recent post where an owner ran into this same problem.
He bought the Kel-Tec barrel nut tools and attempted to get the lower nut off so he could replace the lower sight base.
Unfortunately the Kel-Tec tools failed to get the nut off and he had to send it in to the factory for repair.
Due to the design of the lower base and nut, it takes a unique tool to remove the nut and the Kel-Tec tool just doesn't seem to be up to the job.
Read this thread............
New owner of a KS7. Field stripped, wiped down all the assembly/shipping lube, and lightly reapplied with my lube of choice. My question is, with a general field strip, you can't get the bolt carrier assembly out. The action bars and bolt carrier could probably use occasional cleaning and...
www.thektog.org
This is one of those cases where it's probably best to cut to the chase and send the barrel in to the factory so they can replace the base.
