Wishbone style 'locking' tension wrench, stainless steel, from SouthOrd.  Spread the jaws of the tension tool so that one tip is at the far upper point in the keyway and the opposite jaw is right at the bottom.  Slide the tiny washer along the wrench until it applies enough locking pressure to freeze the jaws in place.  Provides more room to introduce your picking tool, and a bit better control over tension.