Sandpaper Grades with "P". What's the point!!

[Bob B.]

Hi all,

I have sandpaper for body and paint work with regular numbers like 400 and I also have paper with the number with a P before it, such as P400. The P400 is notably coarser than the 400. I thought maybe the P was for sanding primer, but I wondered then why not just use a coarser sandpaper for sanding primer since the P400 is obviously not 400.

Over time, I have collected up quite a bit of "P" sandpaper and it is always coarser than the equivalent number without the P, so I finally decided to Google it and, turns out, that the "P" sandpaper is a European system that is only fortuitously numerically equivalent at very coarse grades. At higher numbers, all the P sandpaper is coarser than the equivalent American grade.

So, am I the only one who noticed this?? P1200 is the equivalent of American 600!! If I had not noticed that the "P" sandpaper was coarser, I could easily have gone from 800 American and unknowingly back to 600 by using the P1200 and ruin my paint!!

We live in America, so what is the point of having a European grading system on half of our sandpaper, with no comment whatsoever, no conversion, no nothing? If I buy a liter soft drink, at least it says 1.06 quart right on it.

I see no reason for something like this, but I am ready to be educated as to the benefit of having of sandpaper with a European designation and, if there is one, why can't 3M put both European and American grades on it, so I don't have to look it up and find a conversion chart?

Does everyone in American already know this and are fully conversant with mentally doing the conversions, and I, as usual, am the last to know?

Thanks,

Bob

[Mike F.]

Re: Sandpaper Grades with "P". What's the point!!

Sounds like a stealthy and calculated power grab by the European Union. What's next, temperature in C*?

[Bob B.]

Re: Sandpaper Grades with "P". What's the point!!

So, I take it you have no idea, either.

[Russ S.]

Re: Sandpaper Grades with "P". What's the point!!

Thanks for the info Bob. I hadn't heard that before.

[Edward B.]

Re: Sandpaper Grades with "P". What's the point!!

I wasn't aware of the "P" designation either so I did an internet search for "sandpaper" and came up with this: https://en.wikipedia.org/wiki/Sandpaper
Being Wikipedia, certain cautions should apply, but it does seem to explain the differences.

[Kenneth P.]

Re: Sandpaper Grades with "P". What's the point!!

Much like the standard vs. metrics we apparently have US and the European sandpaper. Most automotive parts stores, that I know of, sell both types of paper and to be honest I didn't know the difference until now. Thanks for starting this thread.

Here is an excerpt from the link below.

"However, different countries, manufacturers or even products use different systems so there are a few different Grit systems. Most of the sandpapers in market are using the International Standard, which is based on FEPA (Federation of European Producers of Abrasives) P- Grit system for coated abrasive."

http://www.ebay.com/gds/Guide-2-Choosing-Sandpaper-What-Grit-to-Use-/10000000176926001/g.html

[Duke W.]

Re: Sandpaper Grades with "P". What's the point!!

Prior to attending the hyperloop competition at SpaceX last Sunday (I was invited by the U. of Wisconsin ME Dept. Chairman.) I had to bone up on SI pressure measurements, particularly the Pascal.

One Bar, which is 14.5 psi is 100,000 Pascals, and a one Pascal is one Newton per square meter, and a Newton is 0.225 pounds.

So my first question to the U. of Wisconsin team was: What's the pressure in the tube? And the answer is 800 Pascals, which is about .12 psi. I thought that's about the same as the surface pressure on Mars, and my buddy looked it up on his smart phone - 600 Pascals - about .09 psi.

I tried to look up what altitude this would be above the earth's surface. I figured something over 100,000 feet, but the pressure tables on the Web only go up to about 65,000 feet.

Some pods have a seat, but only a manikin rode along as they are not pressurized, however, my thought was that if a real hyperloop ever gets built, loss of pressure in the pod means everyone aboard is dead in about a minute.

I don't know if Elon Musk has thought that one through.

Duke

[Don H.]

Re: Sandpaper Grades with "P". What's the point!!

I can't speak for Mr. Musk, but I am having trouble thinking your post through.

[Michael W.]

Re: Sandpaper Grades with "P". What's the point!!

I find some of the comments in this threads to be quite abrasive.

[Duke W.]

Re: Sandpaper Grades with "P". What's the point!!

I can't speak for Mr. Musk, but I am having trouble thinking your post through.

Don't worry. We won't be around if/when a commercial hyperloop ever gets built.

Going OT, but Musk's idea of a hyperloop between LA and the Bay area makes no economic sense. The one-hour flight from LAX to, say, San Jose could be cut to maybe 40 minutes. But consider a hypothetical trip from Anaheim to Silicon Valley.

The 35-mile trip in the morning from Anaheim to LAX will take one to two hours depending on traffic, accidents, etc, so figure an average of 1.5 hours. A hyperloop could cut this to about 10-15 minutes, so for one tenth the cost based on miles, a 35-mile hyperloop between a central point in OC and LAX saves more time than a 350-mile hyperloop between SoCal and the Bay Area.

Musk is a good salesmen, but he reminds me of the "futurists" from the fifties and sixties. I'm still waiting for my flying car.

The trouble with short trips between major population centers like LA and the Bay Area and New York and Washington is getting from your origin to the airport and from the arriving airport to your final destination. The plane ride is usually the shortest and easiest part of the trip.

Duke

[Don H.]

Re: Sandpaper Grades with "P". What's the point!!

thank you Duke, but I still don't know what a hyperloop is and how it's relevant to the P on sandpaper. And I don't know any Newtons or Pasquales, nor have any interest in the surface of Mars, unless there are mid-year corvettes up there, especially 64/65 FI cars.

[Siegfried K.]

Re: Sandpaper Grades with "P". What's the point!!

Thank you Bob for the clarification. This is very good information to be aware of. That sure explains some of my sanding results in the past.

[Edward J.]

Re: Sandpaper Grades with "P". What's the point!!

thank you Duke, but I still don't know what a hyperloop is and how it's relevant to the P on sandpaper. And I don't know any Newtons or Pasquales, nor have any interest in the surface of Mars, unless there are mid-year corvettes up there, especially 64/65 FI cars.

Don sound like were really heading toward the Jetsons age.

[Gene M.]

Re: Sandpaper Grades with "P". What's the point!!

Thank you for the posting.
I never purchased P sandpaper.
I didn't know of it.
So now I never will buy P sandpaper.
Good information.

[John L.]

Re: Sandpaper Grades with "P". What's the point!!

Sirs:
sandpaper chart US vs Europe