I've always worked with the numbers of between .045" and .055". That seems to satisfy most every spec I've come accross. If they're between those specs, I'm satisfied with it. If I'm fitting a new one or adjusting one, I usually set it up a bit less,,around .040", not that it makes that much difference. Just something I do.
I've had them alot less,, in the .030 range and they still seem to work fine. The less the better to avoid any primer puncture, but yet get good reliability.