Since you asked:
the SSMB8 require a MINIMUM of 1/2" spacer on HiFi or Logic 7 enclosures/
For BASE "Stereo" enclosures, a minium of 3/4" in is required.
Additionally, the cutout hole diameter must be NO MORE than 7/25" or you will have issues lining up the screw holes into MDF.
Just wanted to throw that out there as I originally ordered the 1/2 for mine and had to change them.
Edit: JTsherri is indeed a great member (non-vendor) seller.