Re: Difference between G type ISO228/1 and Rp ISO7/1 !!!
In this context which are the difference between a G type ISO228/1 internal parallel thread and Rp ISO7/1 internal parallel thread? When we must use G type and when Rp?
Gordon is correct:
"When a pipe thread is made to be pressure tight a ISO 7-1 pipe thread (R) uses packing tape or packing garn etc. while an ISO 228 pipe thread (G) is made pressure tight with an O-ring or fiber gasket etc." Thus which you use and when is a decision made in the product design stage. The product engineer should have made this clear on the part print.
I have been in process of building a webpage:
G vs. Rp, but it is still under construction. Someone reading this post in the future will have the benefit of the webpage, but for now: Sorry.
A quick summary:
G and Rp have the same basic dimensions.
G thread tolerances are all to the positive.
Rp has the same positive tolerance plus an equal minus tolerance.
About the thread gages for these threads:
G threads require GO/NOGO style gages
Rp threads, per ISO 7, are checked with Rc plug gages
Unofficially some people have GO/NOGO style gages made for the Rp threads.
Based on that, if you need to make Rp threads, you can use G gages and you will be within tolerance.
Conversely; if you need to make G threads the resulting part may be out of tolerance if Rp GO/NOGO parallel gage, or Rc taper plug gage is used.

The above is my opinion based on my reading of the standards. If you are going to be risking much money, I suggest that you purchase copies of the standards and do the research.
I hope this helps.
