Drill bit/tap size for 3/8" bspt boost gauge tapping

[Paul_13]

It's been a very long time since I dealt with these kind of things (back in college 8years ago) 

I've ordered a brass bspt adapter 3/8 tapping with 1/4" hose connection. 

Now logic tells me to use a 9.5mm drill bit? Which is what size 3/8" is roughly. Do I just use the barb as a tap or do I need to use a proper tap? 

[Iceman299]

I would use a 6.5-7mm drill bit and a proper tap to make the thread (making sure the pitch is the same)

[Dum-Dum]

Google suggests somewhere around the 15mm mark?!?!?!?
https://www.google.co.uk/webhp?sourceid=...drill+size



Personally I'd buy an M8 or M10 bleed nipple and drill for a standard metric thread (M8 can be done with a 6.5mm bit that most people have)

[shervo]

I used a 1/8 bsp taper tap with a 1/8 bsp taper nipple and used a 8.6mm drill. If thats any help.

[Paul_13]

Google suggests somewhere around the 15mm mark?!?!?!?
https://www.google.co.uk/webhp?sourceid=...drill+size


Personally I'd buy an M8 or M10 bleed nipple and drill for a standard metric thread (M8 can be done with a 6.5mm bit that most people have)

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I saw that as well and I really didn't think it was right, hence asking on here

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I think I'll change my approach to this

[Poodle]

Aren't bsp sizes stated at X-1/8th, X being the actual size? So 3/8bsp is actually 1/2"? I may be thinking of npt...

[C2K]

Be careful with BSPF, BSPP and BSPT. BSP is a pipe thread form and therefore the size can be misleading. It used to denote the pipe bore, but it doesn't really work nowadays. Taper tapping size is smaller than BSPF or BSPP tapping size.

3/8 BSPT tapping would be a bore of 9.525mm, but tapping drill for that size is 37/64 aka 14.75mm.
http://www.tradezone.co.nz/tapanddie/dri...pt-tap.htm

[Paul_13]

Should of realised it was inside bore.

Think I'll re order a m8 nipple

[Alan_M]

Where's your Zeus book?

[Paul_13]

http://m.ebay.co.uk/itm/Barbed-Threaded-...1600317066

I've opted for this.

Lost you there Alan

[Alan_M]

http://m.ebay.co.uk/itm/Barbed-Threaded-...1600317066

I've opted for this.

Lost you there Alan

One of these....Will tell you drill sizes for tapping, amongst other stuff. 

[C2K]

You can get it here, but iirc it's not got bspt in. Mine is at work.
http://www.green-oval.com/data/zeus.pdf

[Paul_13]

Nice, I'll get myself a copy of that

[Paul_13]

http://m.ebay.co.uk/itm/Barbed-Threaded-...1600317066

What I've ordered now. Bit of ptfe/loctite will be all good