On Sat, 20 Oct 2018 17:31:36 -0700 (PDT), Clark Moss
wrote:

What is the minimum recommended bench top thickness when using bench-dogs or other types of hold-fasts?

I'm replacing the top of my work table with some 1.25 inch thick butcher block. I'd like to add some 3/4 inch holes for hold fasts.

Thickness doesn't matter a whole lot for bench dogs. A Black and
Decker Workmate has a 3/4" thick top and they work fine. Where you
might have a problem is with the holdfasts--1.25 is a bit thin for
them.. Try them and see if they hold, if they don't then fasten a
block underneath and drill it through to increase the thickness.

You might find this of interest:
http://www.toolsforworkingwood.com/store/blog/251/title/Some%20Tips%20on%20Using%20Our%20Gramercy%20Holdfa sts