How to Create Vent Hole

You can't get there from here.

You will need a welded adapter, or a Tee.

You can only do this if you know the difference between a vent hole and a blow hole?

Remember, this is a public engineering forum. Keep your answers clean like any good member of the Ancient and Honorable Order of Turtles.

This looks like a vent (or "weep") hole in a reinforcement pad for either a vessel nozzle or pipe branch. If so, the "NPT" is irrelevant; all you need to do is drill a 6mm hole.

thanks mr Tornado,can i drill hole and weld reinforcing pad with pipe after that i tape NPT thread or i must tape NPT before weld reinforcing pad. this hole need tape NPT for pneumatic test, can you advise me select tape (diameter (inch)) to thread this hole

6 mm is not even close to a 1/4 inch nominal pipe thread size which is about 13 mm.

The OP needs clarification from the designer regarding this obscure notation.

Is there some reason you cannot use a thread-a-let fitting on this application?

thanks Mr gringogreg,

you right, this drawing also make me confuse, because 6mm npt can be understood 1/4 " npt,after that must drill 12 mm hole to tape 1/4" npt.But we can also think this hole is 6mm and must be use 1/16 npt pipe tape. I discuss with construction they said tape 1/16" difficultly and they want tape 1/4"

Sonpvms,

Look at my previous post, if you drill a 12 mm hole it will be too big to tap 1/7" npt.

Forget metric sizes stick with Imperial as it is an American standard thread.

Best regards,

John

thanks Jesw55

i agree with your answer, i already bought thread tool to create 1/4 " npt. Thanks for your help

IF your material is less than at least 0.250" thickness, you will probably not have good threading result. You also need to drill the hole, and attempt to tap it prior to removing the workpiece from the drill press or mill. This means you will need vertical clearance to remove the drill bit, room in stand the tap in the hole, with the tap wrench on it, and a live or dead center to fit the dimple on the thread wrench to hold the tap perpendicular to the material (coaxial with the hole). You will not really have more than 2-3 threads to work with on finished product. Good luck.

You would be better off welding a fitting to the work over the 6mm hole.

Good morning. While i cannot speak to the application itself, my interpretation of the port call-out would be that it indicates a 1/8" NPT port. In my experience with one of our Japanese product lines this would make sense, as a -6 when referring to a threaded port would indicate a pipe thread, either BSPT or NPT as specified by the rest of the part number. Also note that the drawing does not technically state that the diameter given is in millimeters. I hope that is helpful, i think you will find that it is correct. Have a great day!

Suggest you just google "drill tap chart". Easy enough to look up.

There is no such thing as <...6mm npt...>; NPT threads are fractional inch sizes.

Bounce the drawing back to the Designer for correction.

As Gringo Greg, Whitephone, and Lyn pointed out, you need a 6mm hole (this is approximately by hand grenade estimate, the inside diameter of 1/4" NPT pipe). However the drill size is 7/16" for 1/4" NPT tap. The tap must be maintained normal to the hole axis for useful threads to result. One also must decide how deep through to run the tap, otherwise the threads will be too loose to be functional, especially when the material thickness is marginal at best.

As with Lyn, you can't get there from where you are, unless you also weld on a threaded adapter over the 6mm hole.