Most Moparheads know that the dreaded term "NS1" means a part is no longer available from the dealer. Once in a while, you may run across other "NS" codes and wonder what they mean.
Wonder no more. According to "Mopar Parts Price List", June 17, 1963:
CODE SYMBOLS NS1 NS2 NS3 NS7 Part numbers coded "NS1, NS2, NS3 or NS7" have been discontinued for service. Substitutions for these parts are not available. Generally, these parts are listed for past models for which there are no longer a demand. (The numerals 1, 2, 3, 7 following the NS code are factory codes and have no significant meaning for field use.) CODE SUMBOLS [sic] NS4 NS6 Part numbers coded NS4 and/or NS6 have been discontinued to service the assembly or service package respectively. These parts should be respecified, using the last edition of the Parts Catalog to determine the proper assembly or service package number required to service the vehicle. CODE SYMBOL NS5 Part numbers coded NS5 apply to assemblies and packages which have been discontinued to service the component parts. These parts should be respecified, using the last edition of the Parts Catalog to determine the availability of component parts required to service the vehicle.