Hi Archephile
It depends on the size of the blade, and probably the depth of the spine, as to what will achieve the necessary stiffness, though 1/4" or so is typical.
Some examples (just approximate)
Gramercy DT - 3/16"
Wenzloff Kenyon DT - 1/4"
LN DT - 1/4"
Adria Carcass - 1/4"
Wenzloff Kenyon Sash - 9/32"
Wenzloff Kenyon Tenon - 5/16"
Interestingly, a 26" Stanley mitre also has a 1/4" (steel) spine, though of course the saw plate itself is very heavy (.04" (1mm :shock: ) compared to say the 19" Kenyon tenon at .026" or the Gramercy DT at .018"
(My calipers need a new battery, so these saw plate numbers are suspect)
HTH
Steve