Correct drill bit for 3/8 npt sump fitting
 

Hey guys,

During a garage cleanup Ive lost the countersink style drill bit that was leant to me...(hurr durr).

The sump fitting Ive got is a 3/8th NPT.

Im Asutralian and (have a sense of humour guys) here in Oz we use a measuring system that makes sense.
I figured out that 3/8th npt tap has a diametre is like 16.8mm, or about 5/8th which is stupid.
And now Im trying to find the right sized drill bit.
It seems that a 37/64ths countersinking bit is about right, but where do I get one of those from for a decent price. And what a ridiculous size!

Anyways Ive searched and found that most people have 1/2npt return fittings so that information doesnt translate.

Thanks heaps.

TL:DR- i have a 3/8th npt fitting and tap for the sump, what drill bit do I use, preferabbly a metric size or an easy to get imperial size.

Thanks,
Dann

Ok, so can a 5/8th be used, because what I used last time was a countersinking bit like this..

https://www.miataturbo.net/attachmen...ine=1333449304

And they seem to come in 1/2 (obviously wrong), and 5/8th.
I remember it looking like it would be too big but being fine in the end.

Dann

Hey Dan,

Why don't you send Begi a quick email and ask what size drill bit is included with their 3/8" Oil pan drill/tap set?

I'm actually going to need the same bit soon to drill my sump, whatever size it is.

According to this thread a 9/16" bit should do the job, so about 14mm (14.3mm).

Everyone should have one of these hung up in their garage:

http://www.brokenbolt.com/images/sta...-tap-drill.pdf

Print it out or get a huge poster of it. Npt is down in the corner, obviously saying 3/8 is 37/64. 9/16 can be used, it's only .015 larger. Keep in mind though, it's a tapered thread you're not supposed to bottom out, so the slightly larger hole wont require the tap going as deep before you go too far.

Thanks guys.

Honestly, imperial makes so little sense its crazy.

Ive purchased a 5/8th countersinking bit and Im going to turn it down to the correct size.

Thanks,
Dann

Also don't forget that the Teflon goo or tape is a libricant to allow the fitting to thread in further. So you don't need a lot, AND, if you're checking the fitting depth as you tap, remember it'll go further during final installation.

Thanks mate,

really appreciate your help.

:)

dann

http://www.toolbox.co.uk/silverline-...ep-15441-86908

I used the 14mm diameter of a stepped drill bit like the one in the link.