What's the difference between 41-902 plugs & ...

41-940 sparks plugs. I have set of 41-940 for a 93 Bonneville with 3.8 that I'd like to use in my son's 91 PA, but the 41-902's are recommended for my 91 PA. However, there are a bunch of plugs that can be used for either car. Any help would be appreciated. Thanks.

BTW All plugs number mentioned are AC Delco.

The first link below, will show you how the numbering system works. The second link, you can enter the part number of the plug and it will tell you what car they may be used in. Be careful, heat ranges vary significantly between plugs, with wide margins in the last set of numbers.

Spark Plug Identification Table | Parts Information | ACDelco (http://www.acdelco.com/parts/sparkplugs/identification.jsp)
Parts Information | ACDelco (http://198.208.187.182/internet/VehiclePartFits.jsp;jsessionid=F0nC0HTK9G%21168275 595%21382668424?autosel=A&part=41-940)