But they all look like 8 - 10s when the beer goggles are being worn.
Found this in BS EN ISO 18275:2018
5 Symbols and requirements
5.1 Symbol for the product/process
The symbol for the covered electrode used in the manual metal arc process shall be the letter E.
In reality there are several problems and the first is language and its interpretation, then we have standardisation, then we have individual standardisation which is individual countries or regions, then of course there is harmonisation such as the EU standards applied to all individual countries, and evolution and I will explain this in loose terms.
If we take the EU, each member state had its own standards and British Standards were the most consistent followed by German standards and then Dutch standards which mirrored the German standards, Spain? if it held it was a weld or their expert welders were superb and there was little inbetween, so everything was harmonised across all member states to apply the same standards to everyone, so a whole region became standardised in everything from machines to consumables and the quality of training and required standards which were to be met and then maintained, but at the time most stick welding was AC and little DC stick was about due to the high cost of DC machines.
Things evolve and as DC machines became cheaper more people bought them as small companies found they were within reach of their finances and you went from a scenario of most electrodes being for AC welding to being AC/DC electrodes and with a range of OC voltages for them to operate within, and more evolution followed as DC replaced AC welding as the go to or default machine and more electrodes became DC biased, and more evolution followed with a wider range of electrodes available such as brazing rods for DC machines as one example.
With the EU harmonised in stick welding the next challenge was MIG welding as MIG became more common and a set of standards were introduced, refined, and harmonised and were generally based upon the wire welding machines such as submerged arc welding for heavy sections in straight lines as this is generally where the compact MIG evolved from as you could get a MIG machine which could stand in a factory and run from an industrial supply as opposed to being connected directly to the power station, industrial sized components could be used to give a 100% duty cycle and the powdered flux was eliminated and replaced by a shielding gas to give an affordable machine which was faster than stick welding and time is money in industry, which was its original selling point. Everything went metric and electrodes changed from guage to MM diameter, fluxes were harmonised along with everything else.
Now everything in Europe was standardised with sufficient scope to tweak things for the future if required.
Enter the world market and EU standards had to mirror or match other world standards as manufacturing went from individual countries to things being built using components from a multitude of different countries and t anyone supplying components to EU manufacturers had to meet these standards to comply with EU legislation so they all modified and adapted their own, similarly, EU countries exporting to other countries had to meet their standards and many other countries changed their standards to give as much overlap between standards between different countries, look at the evidence. One non EU shipbuilder builds the basic hull using steel from Sweden, many components come from Spain, others come from Malaysia, while the rest come from as many as 20 different countries and this is where the large overlap in standards paid off for the client.
language and its interpretation may be more confusing as many standards slecify an individual standard for an individual process such as stick welding and as evolution and world manufacturing came into play they were not specifically specified in terms of a standard language, and many people forget to refer to the specific standards and make assumptions of whey think it means and these assumptions stick; let me give an example, how many people have a vacuum cleaner made by VAX, Dyson, Shark or any other brand and they all call it a Hoover.
The E, R or D in your book refers simply to the method by which the flux is applied to the metal electrode. It is likely that since the book was written, the D method of manufacture has fallen out of use (possibly too slow, too expensive, not consistent enough, etc.). So if every electrode made today has the flux applied by extrusion, the designation actually becomes redundant as you have no other choice. It has therefore morphed into an identifier for a MMA consumable to distinguish it from other-process-consumables.
If you look on YT at electrode manufacturing videos, the bare wire goes in one end of the machine (the sausage) and a long, coated electrode (the sausage roll) comes out of the other. It is then chopped to length, the uncured flux removed from the stinger end and then baked to cure the flux.
Thus is wild speculation but the R designation sounds like it might be used for specialised electrodes with a particularly thick flux on them (someone posted pictures of a 3/4" dia. one) where the flux might be too fragile if unreinforced.
When I worked at an electrode manufacturers,the filler wire was precut.
Separate names with a comma.