Abstract: A safety valve for use in a well conduit which is automatically actuated to close when production flow impingement on a retrievable flow choke in the safety valve operating tube is sufficient. The safety valve utilizes all metal to metal seals and includes a unique roller detent mechanism, which releasably positions the operating tube in valve open position and provides snap closure of the valve. The operating tube has internal locking recesses and a metal seat. A flow choke of the size to cause safety valve closure at a selected flow rate is connected on a lock mandrel having a metal sealing surface. The lock mandrel with choke is lowered into the safety valve and operated to seal on the metal seat and lock in the locking recesses. When it is desirable to change the choke size, the lock mandrel is retrieved from the safety valve to surface.