Bruce,
The gun in question has back action locks. I suspect that this is a mainspring cramp. When the locks are dismounted and the hammers are cocked the cramp is placed on the mainspring, then the sear is released and the hammers are let down, but the spring is still compressed and the spring can be removed from the lock for a complete cleaning. When the cleaning is done the process is reversed and the lock reassembled and is ready to go back into action.
But I could be wrong, would need the locks and the tool in hand to prove the point...
Bob
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Bob Roberts
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