Spark plug difference - AC DELCO 41-110 and 41-993

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Any difference between the AC Delco 41-110 and 41-993? I just called Michigan Motorz to get their recommendation and the tech said that the 41-110 was a hotter plug and recommended I use the 41-993.... The guy that sold me the 41-110 plugs said there's no difference. If it is in fact a hotter plug, maybe that's the cause of the slight knock/ping i'm hearing? Gonna pick up the 41-993 today and swap them out but wanted the forums take on this.
Thanks