Metal Composition: 91.67% Gold - 3% Silver - 5.33% Copper
Diameter: 16.5 mm
Mass / Weight: 3.393 grams
What This Coin Looks Like (Obverse, Reverse, Mint Mark Location, Special Features, etc.): There are two major varieties of the 2015 $5 Gold American Eagle. The less common variety is known as the "Narrow Reeds" variety and the more common variety is known as the "Wide Reeds". The difference between the two coins depends the thickness of the reeds on the edge of the 1/10 oz $5 gold eagle. The "Narrow Reeds" are much finer than what the reeding normally is for $5 gold eagles. Experts say the US Mint was using a narrow reeds collar for $5 gold buffalo coins being minted in 2008 and they began experimenting on using this for gold eagle starting in 2014.
The difference between the 2015 Narrow Reeds vs Wide Reeds is depicted below in the example comparison image (Source of example images is courtesy of NGC):