discustion for pipe thickness

I found this government publication on pipe.

1. All pipe is to be made of a long hole, surrounded by metal or plastic, centered around the hole.

2. All pipe is to be hollow throughout the entire length - do not use holes of different length than the pipe.

3. The ID (Inside Diameter) of all pipes must not exceed their OD (Outside Diameter) - otherwise the hole will be on the outside.

4. The pipe is supplied with nothing in the hole, so that water, steam or other stuff can be put inside at a later date.

5. All pipes is to be supplied without rust; this can be more readily applied at the job site.

NOTE: Some vendors are now able to supply pre-rusted pipes.
If available in your area, this product is recommended, as it will save a great deal of time at the job site.

6. All pipe over 150m in length should have the words "LONG PIPE" clearly painted on each side and end, so the contractor will know it's a long pipe.

7. Pipe over 3000m in length must also have the words "LONG PIPE" painted in the middle so the contractor will not have to walk the entire length of the pipe to determine whether it is a long or short pipe.

8. All pipes over 1.8m in diameter must have the words "LARGE PIPE" painted on it, so the contractor won't mistake it for a small pipe.

9. Flanges can be used on pipes. Flanges must have holes for bolts, quite separate from the big holes in the middle.

10. When ordering 90 or 30 degree elbows, be sure to specify left-hand or right-hand, otherwise you will end up going the wrong way.

11. Be sure to specify to your vendor whether you want level, uphill or downhill pipe. If you use downhill pipe for going uphill, the water will flow the wrong way.

12. All couplings should have either right-hand or left-hand threads, but do not mix the threads, otherwise, as the coupling is being screwed on to one pipe, it is being unscrewed from the other.

13. All pipes shorter than 3mm are very uneconomical in use, requiring many joints. They are generally known as washers.

14. Joints in pipes for water must be watertight.
Those pipes for compressed air, however, need only be airtight.

15. Lengths of pipes may be welded or soldered together.
This method is not recommended for concrete or earthenware pipes.

16. Other commodities are often confused with pipes. These include; Conduit, Tube, Tunnel, and Drain. Use only genuine pipes.