Hmmm Interesting... Also from Silver Audio's website..
"Silver Audio is therefore thrilled to offer the solder-less, TopLine WBT locking RCA connector as an option for the 4.0s and 6.0s. WBT is universally regarded as the Rolls Royce of Audio connectors and their model 0108 represents the top of their line. This cost-no-object connector features the most powerful locking mechanism in the business and is precision machined in West Germany to exacting tolerances of <2/100 mm! The base metal is an extremely conductive, proprietary alloy based on over 99.996% pure copper....."
Maybe copper can be more than 99.99% pure.
"Silver Audio is therefore thrilled to offer the solder-less, TopLine WBT locking RCA connector as an option for the 4.0s and 6.0s. WBT is universally regarded as the Rolls Royce of Audio connectors and their model 0108 represents the top of their line. This cost-no-object connector features the most powerful locking mechanism in the business and is precision machined in West Germany to exacting tolerances of <2/100 mm! The base metal is an extremely conductive, proprietary alloy based on over 99.996% pure copper....."
Maybe copper can be more than 99.99% pure.