Hi Mike
The proper tap drill is a No. 7 (0.201)
The nearest fractional is 13/64 (0.203)
If aluminum, I like to stay on the small side so I would use a 7 or an 8
(0.199). If steel, then the 13/64 works fine. The 13/64 works for AL
also but the threads will be a little shallower.
On the real small sizes (no 10 and below) I stay to the large size if only
because the taps break so easily unless it is real thin stuff.
---------
Phil Chambers [ptchamb@No-Spam] (S.F. Bay Area - Calif. USA)
On Sun, 28 Sep 2003, Tony Hurtado wrote:
> Mike,
>
> Looks to me like 7/32" is a little on the large size for a hole you want to tap. Take a look here:
> http://www.efunda.com/designstandards/screws/tapdrill.cfm
>
> I'd try the 7/32", but it's really a little on the large side for tapping. How about 13/64"? It's just about perfect!
>
>
> Good luck,
>
> Tony Hurtado
> N8i in Si Valley
>
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> OT Tap/drill size
> From: Mike J. Shade (mshade@No-Spam)
> Date: Sun Sep 28 2003 - 13:18:34 MST
>
> a.. Previous message: William G. Schultz: "JG and SM: APOD"
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>
> --------------------------------------------------------------------------------
>
>
> Need to tap out a hole for a 1/4-20 bolt...anyone have any idea what size
> is the proper drill? I've got 7/16 and 7/32 from the net, any idea which
> is the right one?
>
>
>
> Mike J. Shade: mshade@No-Spam
> Sonoita Hills Observatory, Sonoita Arizona
>
>
> See work done at the observatory: http://c3po.cochise.edu/astro
> under the "photographs and images" panel on the left of the screen.
>
>
> "I like the dark, it's cheap." E. B. Scrooge
>
>