Hey Carl,

They are made from a steel stamping all one piece with a bead all around for strength.
https://www.flickr.com/photos/advance-design_parts_co/31210555727/in/album-72157631868452754/
The 6-screws protected by the rubber boots are spotted to the stamping.
https://www.flickr.com/photos/advance-design_parts_co/46099519552/in/album-72157631868452754/
The top has a grip tape product attached as one piece.
https://www.flickr.com/photos/advance-design_parts_co/46099518362/in/album-72157631868452754/
They measure 21” x 7-1/2” with a 1-1/2” lip.
https://www.flickr.com/photos/advance-design_parts_co/46150014171/in/album-72157631868452754/