It is exactly the same.
Just drop the first digit from the Wix number to get the Napa number. For example, Wix 51348 = Napa 1348
Napa just puts their own name on it.
Napa silver and Proselect are the lesser quality filters.
Thanks, Tommy...How do I know if I'm getting the "Gold" equivalent?
In Wix or NAPA?
If Wix, there's only one product- the premium one. If NAPA, then look at the number and description. It will say NAPA Gold and have the numbering system as described in the previous post.
The NAPA Silver and Pro Select lines are labeled as such and have a slightly different numbering system (a prefix number added to the 4 digit NAPA number)