The parts studied here are from the electric sets sold, for the best part of the 20’s. They were sold in sets that included the X1 and the X2 set (that also added the motor and accumulator of the day). The parts were also included in the #7 outfits (and 6a's) from 1922 until about 1933 (1935 in some markets!) The electrical parts (and sets) were said to have appeared in Sept of 1920. Typical of Meccano so they were available for the Xmas of 1920. These Xmas sales represented a large portion of the yearly sales for Meccano! Dated sets from this late 1920 time are known and the 1st manual is dated July 1920, so this fits. The sets were not huge sellers and the last of the X1's are dated from around 1928 or so. The X2’s were also not huge sellers and died out a bit sooner...... The parts are numbered 301 thru 315. Not a huge number of parts and they are very simplistic to us now but, in 1920, they represented a huge step forward for Meccano. With waning sales of the sets and very few #7 outfits sold each month, Meccano embarked on a new and better electrical outfit, the Elektron series of sets and parts started in 1933. This required the phase-out of the old 300 series set of parts by late 1933. Some were renumbered and added to the Meccano parts inventory, some were renumbered and absorbed in the elektron’s 1500 series of parts and some were outright obsoleted! This primer uses parts from sets in my collection that includes four X1 sets, two X2 sets, three #7 outfits and one #6a outfit and a box full of spare parts!. All are from the 1920-1928 period. One would think, with so few parts lasting only 10 years or so, they would not vary much......well, there are variations and I will present some of them here. If anyone has anything that looks different than what I am presenting, please let me know. As always, I am always looking for more of these sets and parts and will look at all offers of same......Enjoy!