The Lock Rings tool is used to control ring formation in ring systems and chains. Apply this feature when you want to eliminate search answers in which fragments drawn as chains are included in rings, or additional rings are fused to drawn ring systems.
Click the Lock Rings 
icon.
Click any segment of the ring system or the chain. The entire ring system or chain changes to bold highlighting, indicating that it is locked from ring fusion or ring formation.
Click the Lock Rings
icon.
Click any segment of the locked ring system or chain. The bold highlighting on the ring system or chain is removed, indicating that fusion or ring formation is allowed.
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Drawing and Editing Structures