Here is a  JBL MA15 Speaker Mounting Kit for 8" to 18" Speakers.

This kit will work for two (2) 8"to 18" speakers.

Included in the kit are:

NEW JBL OEM (Original Equipment Manufacturer) cast speaker clamps (8 pieces)

1/4" by 20 by 1and1/2" CORRECT PHILLIPS HEAD SCREWS (8 pieces)

1/4" by 20 four prong "T" Nuts (8 pieces)

PSA Cork gaskets (4 pieces)

 Installation instructions included