Why is a 1/2" Tap Shank Smalelr than a 3/8" Tap Shank?

Dunno.

I myself wonder why "good" taps don't have the shank ground down to less than the thread profile. That would allow you to thread a hole as deep as the tap could reach, rather than only as deep as the threads are cut on the tap. Even pulley taps usually have the shank as large as the thread profile.

...And you're prolly thinking "well duh, it costs more", except that most of the cheapest Chinese sets do it that way....

Look in the Machinery's Handbook. There are specs listed for taps, including the shank diameter. 3/8" tap shanks are larger than 7/16" or

I have yet to get an answer for this..

(It looks like you transposed your round and square dimensions for the

I don't have an answer to your question, but one good result of having different size shanks is that it keeps people in our shop from grabbing the wrong size torque adapter.

DougC wrote: Even pulley taps usually have the shank as large as the

The 1/4 - 20 pulley tap at school has a reduced shank I know because I've used it to tap a very long deep hole several times. I wish we had a 3/8 -16 one to match. :-) ...lew...

Your 1/4-20 is a nut tap. The shank on pulley taps is the same diameter as regular hand taps. The shank on nut taps is smaller than the minor diameter of the thread.

Yes. apparently I did. That and the typo in the subject line (now fixed) makes me wonder how I ever passed a single class in school. :)