What is the reason why the security lock inside the anti theft door lock cannot be screwed?

You can try adding some oil, don't twist it too hard, in case the key is broken, it will break.

I guess there's something wrong with the marble, or maybe it's stuck somewhere...It's not expensive to change the lock body.

The marble chamber in the marble chamber has a special structure corresponding to the pits of different depths of the A and B keys, and a 1mm steel ball is installed between the upper and lower marbles. When the A key is used, the height of the lower marble in the marble chamber plus the height of the small steel ball is just flush with the lock cylinder, so the lock cylinder can be unlocked by twisting the lock cylinder with the A key; When using the B key, just the small steel ball can be pushed out of the lock cylinder, that is to say, the lower bead and the lock cylinder are flush at this time, so the B key can also be twisted to open the lock cylinder (this principle is the same as the mother and son key system), but when the lock cylinder rotates at a certain angle, the small steel ball will be affected by the action of the spring spring, and fall into the blind hole that is cleverly designed on the lock cylinder in advance (this is the difference with the key system), some people call this small blind hole a trap, very appropriate. >>>More

Most of the time the lock cylinder is broken.

The keyhole on the door frame was repaired with a file, and the deadbolt card was too tight, probably the door frame was a little deformed.