I totally fell for these fancy fetter type links! Originally an Art Deco Albert chain, we have added an old mine cut diamond to the inside of the bolt ring, to make a clasp you can wear as a feature. This would also work really well styles as an extender. 
 
Tested as 18ct yellow gold an platinum. 
Weight approx 4.48g 
Length approx 6.75 inches
Width of links approx 2.7mm
Diamond 0.13ct - tested as natural, earth mined diamond
Excellent antique condition