Looking for either a book or online reference for a friend in another country that will have both diameter and thickness of all US coins. All help appreciated.

Guess we'll have to flip a coin-- The two references cited above are significantly different; Penny, 18.8 vs. 19 mm Nickel, 20.9 vs. 21.2 mm Dime, 17.7 vs. 17.9 mm etc.

I think you will find that the data on the thickness table Paddyman posted is probably data for the PLANCHET not the finished coin. Thickness for a struck coin is somewhat meaningless because it will vary at every point on the coin, and it is also a function of the strength of the strike and how well the planchet was annealed. You MIGHT be able to specify a MAXIMUM thickness from measuring the rim to rim thickness of a modern proof. You could probably calculate a MINIMUM thickness using a minimum weight planchet, the spec diameter and the specific gravity of the alloy. The SG and weight tells you the volume, from the diameter you can calculate the area of the face, From the volume and and area you can calculate what the thickness would have to be to give you that volume. That gives you the thickness of the blank. (I am assuming the blank has the same diameter as the finished coin, when the edge if the blank is upset the diameter of the planchet is reduced so it is less than the diameter of the blank/coin.)

Diameter and weight are the most accurate specs to use for US coins, at least for coins struck with a collar. As Conder said strike pressure will have an effect on thickness. Also verticle die misalignment will cause variations in thickness. The best reference for weight and diameter is the Redbook.