[size=large]BigTom,
Will try to explain what you are asking (I think).
I have both the AT Pro and AT Max.
ALL GARRETT coils work equally well on both the Pro and Max.
Now the NEL and Cors coils work great on the PRO I line the NEL sharpshooter on my PRO.NEL and CORS DO NOT have coils for the MAX (YET) they are building them just not out yet.
Some Nel coils seem to work on the Max and some don't. I took mine to Garrett's and they tested my NEL and told me my nel would NOT work on my Max because it was to far off freq.
Garrett uses software built into the machine, PRO GOLD MAX, to tune the coils to that machine.
NEL / CORS have to wind/Tune there coils to each machines freq. Pro 15 / Gold 13.6/ Max 18.6/
Hope this makes sense and helps. If you want a nel coil, just wait a little while they will be ready soon so NEL told me.
BTW I love the 6x9 concentric Garrett on my Max
Buddy_TX[/size]