/58 specifies a particular type of electrical connector contact, specifically a pin, crimp removable contact, often referred to as a standard duty pin contact. -363 specifies the contact size (Size 20), wire gauge range (20-24 AWG), and contact plating (Gold). M39029 identifies a US military/aerospace standard for electrical connector contacts, also known as MIL-C-39029 or SAE-AS39029.