3/8 H2 Tap?

Looking to buy a 3/8 X 24 H2 Tap for my wing struts barrels any body know a good place to buy these, I bought one off ebay and when it got here is says 3/8 by 24 but the threads are not even close, its more like a 7/16, maybe I am doing something wrong,

I got some H2 taps at use-enco.com, good price, good selection

Something this important, don't go cheap.

Go to Fastenall or a similar industrial supply store and buy a premium tap, MA Ford, Starrett or similar.