1/2 - 20 please...
I am quite certain that the thread on OD of the 1/2 inch drill we have in the kit this year is 1/2 - 20 (not 1/2-16 as stated above).
If you want to use a similar coupling to last year's with this year's drill shaft, I recommend using the following coupling:
61005K52
One-Piece Clamp-On Coupling Steel, W/O Keyway, 3/8" X 1/2" Bore, 1-1/8" OD
$ 20.76 Each
This will allow you to open the hole on the 3/8 side to the appropriate diameter for the 1/2-20 tap. My machinery's handbook has the hole size as 29/64 (.4531").
The tap is a National Fine (NF) tap so it may be a bit rarer than usual. McMaster has them though:
26955A57
High Speed Steel Hand Tap Bright Finish, Plug, 1/2"-20, 3 Flute
$ 11.41 Each
Good Luck,
Joe J.
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