So in this picture I am asking about the representation of the Plug and Jack. Where does the idea that the plug is rounded on the back side come from? I am trying to put together a best practices doc fo work and was asked for some backup as to who made that standard and I cant find an explanation.
I am not sure where those exact symbols came from. However you could use the ISO Standard:
01.080.40: Graphical symbols for use on electrical and electronics engineering drawings, diagrams, charts and in relevant technical product documentation.
From ISO.org
Found here Link
Or the ANSI Standard (Depending on your intended audience).
First, your arrow symbols are not quite correct. They are not indicative of Plug and Socket as a Plug or Socket can contain Male (Point) or Female (Reverse Point or Cup) contacts. A PLUG is on a flying lead or cable, and a JACK is on a fixed part or assembly.
This came about during WWII. Pilot headsets, Morse Code Key Sets, etc. all used 1/4" Plugs. The rounded back on the Plug was due to the back cover having a curved edge so as not to cut operators, catch clothing, etc. So, the symbology stuck. This is the way I have always identified my connectors, and this is what I teach College students today.
Anything that does not normally move and/or is tied down has a JACK on it. Anything that can move and/or is removable such as a wire harness has a PLUG on it. They can both have either/or male or female contacts.
The closed Arrows pointing up / down came partly from a drawing of a complete cable assembly and indicated ONE PAIR of wires. Probably a headset symbol.
