Couldn't you google that?
"Here's the best breakdown:
#10 tongue = about a 140 traditional flex
#8 tongue = about a 125/130
#6 tongue = about a 100/110
#4 tongue = about 80
As someone earlier noted, the liners themselves add to the boot's overall stiffness too, so if you put a #10 tongue on a Classic, it won't be quite as stiff as an out of the box Seth boot because the liner of the Seth is way stiffer and firmer. Bear in mind that the whole point of FT's 3-piece design is to provide an unimpeded flex pattern, so a #10/140 tongue might feel softer only because it's actually flexing the way it should."
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