E indicates electrode for arc welding.
The first two (or three) digits indicate tensile strength (the
resistance of the material to forces trying to pull it apart) in
thousands of pounds per square inch of the deposited metal.
The third (or fourth) digit indicates the position of the weld. 0
indicates the classification is not used; 1 is for all positions; 2 is
for flat and horizontal positions only; 3 is for flat position only.
The fourth (or fifth) digit indicates the type of electrode
coating and the type of power supply used; alternating or direct
current, straight or reverse polarity.
The types of coating, welding current, and polarity position
designated by the fourth (or fifth) identifying digit of the electrode
classification are as listed in table 5-4.
6) The number E6010 indicates an arc welding electrode
with a minimum stress relieved tensile strength of 60,000 psi; is used
in all positions; and reverse polarity direct current is required.