OK - this is one of my favourite "mystery weights"
... doesn't show up in any publication I'm aware of, but fairly frequently on ebay (got one myself). I have seen one auction with a certificate, stating "Butterfly Silhouette" as name, and Colin Terris as designer - but usually it is referred to as "Mini Butterfly"; "mini" as there is a larger version of almost identical design around, but I have seen only one to date.
The first date cane I have seen in it is 1983: the story goes that due to insufficient capacity at Caithness the weight was produced at J-Glass (John Deacons) for Caithness. As J-Glass closed in 1983 the later weights (latest one I have seen so far was 1993) must have been produced somewhere else, possibly actually the Caithness studio.
The weights show up faceted and unfaceted - with the unfaceted version usually marked as second (CIIG) - but your's doesn't seem to be marked, and as long as we don't have an official description, it cannot be excluded that also an unfaceted version was sold as first quality.
Now - if this is a Caithness weight, designed by Colin Terris, as stated on a certificate (which looks genuine to me) - why doesn't it show up in any sales material, nor the Charlton catalogue? One suggestion was, it was made for the US market only - but to be honest, I just don't know. Any further info on this weight would be most welcome.