Standard Depth For NPT Thread?

[Mickey_D]

I do three different parts that have a 1/8" NPT feature, and the thread depths are different on all three at customer requests (they are for little plastic vent ports) but I have a new part that came in and they want a "standard" depth thread for what looks like a grease zerk. Anyone know what a standard depth for 1/8" NPT is?

[Mud]

Not sure if there's another spec, but I have a thread gage with go and no go flats on the handle end of the threads to gage the depth.

[Gordon B. Clarke]

I do three different parts that have a 1/8" NPT feature, and the thread depths are different on all three at customer requests (they are for little plastic vent ports) but I have a new part that came in and they want a "standard" depth thread for what looks like a grease zerk. Anyone know what a standard depth for 1/8" NPT is?

According to ANSI/ASME B1.20 it's 0.1615" for handtight engagement.
Effective thread length is 0.2639" for an external thread.
The overall length (start to finish/vanish) of an external 1/8" NPT is 0.3924".

BTW handtight and effective aren't the same thing

Gordon

[benedict leighton]

Technical Information : NPT Thread Data Chart

gordon was too fast

[Gordon B. Clarke]

Technical Information : NPT Thread Data Chart

gordon was too fast

But yours is better

Gordon

[SND]

Usually about 6 turns down from the top end of a properly made tap. aka " leave 6 threads sticking out ". Normally that's right about where a gage will sit just where its supposed to.

[Gordon Long]

Another way that I was taught is to hand tighten a standard fitting into the hole and count how many turns it takes for it to come out of the thread. It should take 3½ to 4½ turns for it to disengage. Another thing we do in the shop is mark the flutes with bright red nail polish to show how deep the tap should go for a standard depth.

[rons]

It should take 3½ to 4½ turns for it to disengage. Another thing we do in the shop is mark the flutes with bright red nail polish to show how deep the tap should go for a standard depth.

This has bothered me, especially when I get some SMC regulators or filters and thread engagement does not even go past 1 turn.

[Gordon Long]

There are some specialty fittings with less engagement based on geometry where the fitting can't penetrate into a cavity but for standard plumbing and hydraulics, my methods have served me well. Another thing I have on the shelf is pipe taps with the ends ground off to allow me to get a larger thread diameter in a shallow hole. I start the thread with a standard pipe tap and then cut larger with the shortened tap. If you're doing CNC work, thread milling allows you to adjust the diameter to whatever you like.

[johnoder]

Here is something someone labored over:

http://img.photobucket.com/albums/v3...r/PipeData.jpg

[steverino]

The machinists Handbook has the info you need, but I always use a pipe theread gage. It's the easiest way and you don't have to worry about each person's different definition of "hand tight".

[oldbrock]

I've always left 7 threads showing on the tap for 60+ years with never a complaint or failure. Peter

[El Mustachio]

All good responses so far. Just throwing out another resource for any takers. The FPS "Lightning Reference Handbook" has a handy one page discourse on Pipe Thread (American Standard).

https://dl.dropbox.com/u/39061598/Pipe%20thread.pdf