Recone kits for the N3.X line of subwoofers
 
N3.5 uses 2 or 3 spiders
N3.7 uses 3, 4, or 5 spiders
N3.9 uses 4 or 5 spiders.
 
Increasing spider count will increase FS and reduce VAS while increasing mechanical power handling.  But it changes the QTS value as well and can make a driver not as suitable for SQ applications.  Yes, you can use a 5 spider pack on a N3.5 but then the QTS increases drastically and may not be usable for all applications.  Fi Car Audio is not responsible for "optimal" options choices for your recone needs.