3a Front Wheel Assy 

Spoke size
The approximate dimensions of the spokes have been measured on an assembled wheel (see photographs) and are as follows:
At both sides: 10  1/4".
The height of the nipple sticking out from the rim towards the hub: 12 mm.
Spoke Diameter: 2,7 mm 
The wheel is fitted with 2x20 spokes.

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Giovanni and Paolo Orlando have spoked the wheels of their Neracar and came up with the following dimensions:

Number of spokes per wheel = 40
Length of Spoke = 10 1/4"
Gauge of Spoke = G12 -> 2.60mm (.104” dia)
Angle of Spoke = 80 Degrees
Length of Bend of Spoke = 3/16"
Nipples = 12G  13mm

 Main visible differences are length of spoke (L) and length of bend of spoke (a=B).
The Diameter of 12G spokes appears to be changing depending on website. It doesn’t make much of a difference and I remember the man who made the spokes for the Orlando asked them to be sure about the nipples because he's aware of differences. As long as spokes and nipples are ordered at the same shop it should be ok.

 Reference: http://www.central-wheel.co.uk/spokes/spokes.html

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General information from a different source, with a slightly different way of measuring:

Spoke sizes are as follows:

Please note that the values in mm are approximations, as U.S.Steel Wire Gage, British S.W.G and Birmingham Gauge differ slightly.