1/2" NPT Tap/Drill Size

[StinsonPilot]

For you machinists out there, I'm tapping a piece of aluminum for a #10 AN fitting to move my inverted oil pick up to the vacuum pad.

The 1/2" NPT Tap calls for a 45/64" drill. I drilled the hole to that size, ran the tap into it, but it will only go so far. The bottom of the tap just barely comes out the bottom of the hole, and it just won't turn any further.

This isn't big enough for the fitting, it'll only go in about 1/2 turn. Looks like I need to go deeper with the tap, but it will not go any further. I'm thinking a bigger hole. I saw somewhere that a 3/4" drill was an alternate size for that NPT thread.

My aluminum plate is about .600" thick.

Help!

Thanks guys...

 

[will moffitt]

 

[StinsonPilot]

 

[christopher]

 

[pigpenracing]

 

[Neil]

 

[Grumman AA5]

 

[freerangequark]

 

[MTChris]