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8-40 tap drill size?

What size (letter or number) drill is used for 8-40 tap? Repairing a damaged scope mount on my Mauser. I found my dad's old box full of tiny taps and dies and it's full of lettered and number drill bits.
 
According to Machinery's handbook, an 8-40 needs a #28 which is 0.1405. A 9/64 is close enough at 0.1406. I use a 4-flute 9/64 carbide end mill to drill out 6-48 holes.

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