These may help.
A penny is 0.750 inches in diameter or 19.05 mm
A nickel is 0.835 inches in diameter or 21.21 mm
1/8 of an inch = 3.175 mm
1/4 of an inch = 6.35 mm
1/2 of an inch = 12.7 mm
1 inch = 25.4 mm
Gold…is a primary metal. Which means that pure gold consist of nothing but gold atoms. Gold in its natural appearance exhibits a vivid luster, but the nugget itself is exceptionally soft. Another characteristic of gold is that it can be easily fashioned with proper tooling. Unfortunately pure gold is far too soft of a material to ever be used in making jewelry, simply put; it could never withstand the rigors of daily use. Instead the majority of today’s jewelry is made from a mixture of metals that’s referred to as “gold alloy”. Alloys are an amalgamation of any two metals. Gold alloys are a combination of pure gold and most often silver, copper or tin, hence 99.9% of gold jewelry created today is from a gold alloy of some type.
Labeling Gold Content…the Karat classification is employed in calculating gold content in the United States. Pure gold is classified as 24K gold, this is the highest classification in the Karat System and there are no such CLASSIFICATIONS as 25K, 26K and 28K Gold, anyone endeavoring to market or advertise to you these classification, is a corrupt merchant that is using his or her knowledge to steal form you, the uninformed consumer. Karat refers to the number of gold parts verses the number of other metal parts in the gold alloy. A 10K Gold item contains 10 parts gold and 14 parts of another metal to equal (24k). 18k = 75% Gold, 14k = 58.3 % Gold, 12k =50% Gold and 10k = a total of 41.6% Gold.
Gold Plated Jewelry…Plated jewelry contains a base metal most often these base metals are steel, copper or brass, these metals now have a thin deposit of gold applied to the top. Thus the actual “gold” value applied during the plating process is mostly less than enough to actually be stamped with a karat weight, regardless of actual karat weight being used in the plating process. (12k, 14k, etc.)
Gold Filled Jewelry…is manufactured by applying one or more sheets of solid gold 14K, 12K, etc. and enfolding them under compression onto a base metal to be used in the making of jewelry. Hence the gold sheets are now successfully “filled”. Gold filled jewelry will often have a quantifiable volume of gold in it. There are items where the weight of the gold is actually stamped due to its higher content, of measurable gold. In the case of a 1/20 12K Gold Filled marking it would mean that 1/20 of the gold weight of the item consists of 12K Gold.
As For Silver...It is like “Gold”, in that “Silver” is also a primary metal and pure silver consisting of nothing but silver atoms. Silver alloys are created by combining pure silver and another metal, the most common one used in the manufacturing of quality jewelry today is “Sterling” silver. This silver consists of 92.5% pure silver and 7.5% of some other metal in most cases it is copper, however on occasions zinc will be used in place of copper. The preferred grade of Sterling silver used in the making of fine jewelry is 92.5% pure silver. Hence the mark would be “.925” which is used to designate the level of sterling silver used. For the simplification of explanations you can replace the word Gold, with the word Silver in most categories, i.e. “Filled (Gold/Silver) Jewelry” “Plated (Gold/Silver) Jewelry”. One exception is Nickel Silver which is defined by an array of different names. Unfortunately to an inexperienced consumer the appearance is frequently mistaken for silver. But be sure of this, Nickel Silver has NO silver in it. Nickel Silver is a metal alloy which is created by combining copper, nickel and other metals. This alloy is used extensively in the manufacturing areas of Latin American and Mexico. Most of this jewelry is sold by vendors to sightseers and vacationers visiting their areas.
Important, terms like finished or toned, simply mean that the item/items being described have had their color painted or dyed onto them and that piece itself has no real gold or silver in them.
Vermeil…this is another category of gold finish, which is used in the manufacturing of jewelry, tableware, along with other items used in the home decor. Vermeil is enunciated as “ver-may,” and is an amalgamation of silver and gold. The gold percentage required needs to be approximately ten karats. Most people upon a visual exam will say it is gold they are looking at; this is because though the vermeil may be less expensive than that of gold, vermeil can be polished to a high gloss like solid gold. In the gold plating process base metals are used, they are usually steel, copper or brass these base metals will have a very thin deposit of gold applied to the top. Gold Filled jewelry has a higher gold value, than that of gold plating. Though the base metals may still be a brass or copper metal, the outer layer of the base metal will actually bond with the sheets of gold that are being applied, for the most part 14 karat gold sheets are used. These gold sheets will not strip off and they provide for a higher quality product than that of gold plating Likewise the gold filled process is still a far less-expensive alternative to that of a solid 14 karat gold product. Now with vermeil jewelry it has a base metal of sterling silver. This silver is then plated, using considerably thicker coatings of gold than either one of the plated or the filled processes already described, frequently using as much as 50% more gold. Although this process is less costly than that of solid gold jewelry, it is still more costly than either gold plated or a gold filled item, since the combined price of both the gold and sterling silver will increase the overall cost of the product, but also increase its "real" value.
Palladium...which is also in the platinum family, and thus it is often mistaken for the more costly platinum. Platinum is also like Gold, and Silver in that it is a precious metal. Because palladium shares this kinship to platinum, palladium it is similarly utilized as a manufacturing catalyst and is a popular metal in today’s jewelry manufacturing. Both palladium and the alloy known as white gold are mutual and essential ingredients that are incorporated in the manufacturing of fine jewelry today.
Solid Gold jewelry is simply the Gold alloy itself that creates and holds the design shape.