To get the right size foams, measure the cone diameter and simply choose a kit with a slightly smaller I.D. (inside diameter)

Example:
 In the picture is a 12 inch woofer.  It has a cone diameter of 9.25 inches.  The G12F kit has a I.D. of 8.75 inches giving you a 1/4 inch overlap for glue

FOAM KITS ALSO COME IN 2 STYLES...

  FLAT ATTACH and ANGLE ATTACH.

If you cone does not have a flat lip at the attachment point,
then use a kit with an angled edge.

Example:  

A 10 inch woofer will use either a G10F (flat edge) or a G10A (angled edge)
 

RE-EDGE KIT CATALOG