Thread gages -using the NOGO end correctly.

I'm just throwing this out for discussion... I have my answers from a great source and am proceeding as I feel comfortable to... but I thought the forum may be interested in hearing this...

I'm setting up some a hands-on gage training for new employees at my company (part of new employee orientation). This training will begin with a PowerPoint presentation including the do's and don'ts as well as a visual introduction to the gages... then proceeding to hands on practice.

While I was preparing my material on attribute gages, I remembered we have (what I thought was) a strange rule in our work instruction for thread gages.
The No-Go end is allowed to enter the part up to 1.5 turns.

In questioning the appropriate people at my company about this, I was informed that industry standards actually allow up to 3 full turns of the No-Go end and the dimension is still considered good.

Since the person I spoke with could not remember where they obtained this information, I decided to do some digging to verify the validity of the statement.

I have spoken with two people at Glastonbury Southern Gage (including one of their top engineers) who informed me that it's actually a 3 turn rule for unified (English) threads and for metric, it's 2 turns.
Thus, on an English thread plug, the no-go end MAY enter the part up to 3 turns and on a metric thread plug, the no-go end MAY enter the part up to 2 turns.
He did advise, however, to stay away from using this rule as common practice as to eliminate "gray" areas, but said that it is indeed an industry standard.

Everything I have read on forum posts states that the No-Go end cannot go at all... Feel free to comment.

Re: Thread Gage - No-Go end

jane_ackerman said:

I have spoken with two people at Glastonbury Southern Gage (including one of their top engineers) who informed me that it's actually a 3 turn rule for unified (English) threads and for metric, it's 2 turns.
Thus, on an English thread plug, the no-go end MAY enter the part up to 3 turns and on a metric thread plug, the no-go end MAY enter the part up to 2 turns.
He did advise, however, to stay away from using this rule as common practice as to eliminate "gray" areas, but said that it is indeed an industry standard.

Everything I have read on forum posts states that the No-Go end cannot go at all... Feel free to comment.

Click to expand...

Hi jane_ackerman,

The information you have received is correct, except for one thing - sheet metal has a different requirement - it is 1.54 turns of the no-go gage.

Re: Thread Gage - No-Go end

Thanks for that update Carol.
It's another great day for learning : )

Re: Thread Gage - No-Go end

This is a really fuzzy area, and I've always contended that "industry standards" that aren't officially codified and controlled, (A) can't be referenced on a drawing and (B) are generally useless. What's important is that customer and supplier both understand the requirements, wherever they come from. It's helpful to know that some suppliers might be working under the assumption that the "industry standard" will prevail, so as to guard against misunderstandings, but what really matters is making sure the specifications correctly communicate design requirements. There could be instances where x turns of engagement of the no-go member will be unacceptable, and others, such as relatively deep threads, where several turns might be OK.

Re: Thread Gage - No-Go end

In our org as well we had the practice of accepting 1.5turns across as this was acceptable by all thread standards(English & Metric) I too had never come across the sheet metal. Thats the learning for the day. If I am not wrong (as per the info I have got) they are specified in the IS standard...

Re: Thread Gage - No-Go end

I assume these a straight threads since NPT gauges are step gauges?

Re: Thread Gage - No-Go end

I have attached a photo of the type of thread gage that I was speaking of.
I am not familiar with what an NPT step gage is.
Sorry.

Re: Thread Gage - No-Go end

"NPT" stands for National Pipe Thread. The threads are conically tapered to provide better sealing joints.

Re: Thread Gage - No-Go end

our practice for straight threads is 3 turns.
All our parts are SI units.

Re: Thread Gage - No-Go end - No-Go end is allowed to enter the part up to 1.5 turns

Who changed my thread subject name?
I didn't include the last part that states "No-Go end is allowed to enter the part up to 1.5 turns"
I'd appreciate that being removed, as it is not a true statement and I didn't include it in my original post.
Thank you in advance.