Why nothing inbetween?
Thanks
Quasi
There are values inbetween:
http://www.geocities.com/Area51/Vault/1157/weights.htm
WAG: standard interval weights are used because it looks simpler and easier for consumers (the same reason that we don’t often price things as £0.23, £0.47, £0.61 etc).
Make your own.
Why 2% milk and not 2-1/3%?
Argh. I meant purity, not weight. Sorry.
Most helpful link. I can now impress upon my SO that it really is the thought that counts! 
Quasi
Evidently, 9 karat gold is very popular in the UK and EC countries, but I’ll be damned if I can find it over here.
Being married to an Indian woman, I can tell you no self-respecting Indian would ever consider accepting anything other than 22K. 18K? they sneer upon you.
9 karat gold, at only 37.5% pure, is the lowest grade still legaly considered gold in the UK. My guess would be that in the US 10 karat (still only 41.6% pure) is the lower legal limit.
9 karat is popular here because it is so cheap (and usualy nasty, IMHO)
10K is the lowest % considered “Karat Gold” in the U.S. Essentially, all this means is that as long as you label the contents, you can get away with anything you want.
Karat clad: Trade name for gold coating of at least 100 microinches
R.G.P.: Rolled gold plate- metal upon which gold of at least 10k has been applied, the weight of the Karat gold being less than 1/20th the total weight of the article.
Gold Filled: Same as above with heavier relative weight of Karat gold
Heavy Gold Electroplate: A plating of not less than 100 millionths of an inch of Karat gold.
etc.,etc.,etc.
It would be plausible to assume I could market, say, 7 Karat gold, but:
1: My gold would not satisfy any of the above or other processes requiring “karat gold”.
2: With a low percentage of gold throughout the metal, you are robbed of gold’s natural brightness. It would make better looking jewelry to use gold filled or another process that keeps a high % of gold near the surface.