WW2 "civilian occupation and no" on WW2 discharge papers

[Obsolete_Battleship]

Does anyone have a list of what was on line 21 on the WW2 discharge form? Its easy to find a list of WW2 Army MOSs but I have always wondered what some civilian occupations would have been. My dad was a clerk at a plumbing supply company when he was drafted, was wondering what they army called that and what number.