Throttle plate thickness

Saw someone ask about the different throttle plates on a forum the other day.

So here:

Why are some throttle plates thicker than others?

In the case of 172 and 173 as shown, the thinner plates almost never seal as well.

With closed throttle airflow moving in the primaries more and the secondaries closed, the pull seen at the fuel bleeds is vastly different.

Primary plates don’t need to seal as well as they are going to be held open to attain no load idle speed.

Some carbs like Cobrajets are designed for 172s all around, many tho will be nearly too lean to run if the secondaries bleed off too much air. Not a big deal, but sometimes fuel additions need to be made to end up in the same place.

Anyway, parts were in front of me, thought it was worthy of mention.

107 primary 116 secondary 1 1/2 bore

109 primary 118 secondary 1 9/16 bore

172 primary 173 secondary 1 11/16 bore