Plan to install single runs of 7/8" PEX between solid floor joists in older home. I mapped the runs all out, located the manifolds, counted number and size of holes to be drilled, and asked some friends over for a PEX party to help install after all the holes (1 1/2") were drilled. The joists were all rough lumber and about a full 2 1/4" thick. Many were doubled. Long story, but all help showed and the "expert" began to place the PEX. Suddenly, after his comments that had to do with alignment, I shrunk in a bit of embarrassment. Some of the holes were aligned because I used a template, but many were not. I did not know that the PEX could not withstand a sudden turn in any direction. The PEX had been stored in the boxes that it came in so the amount of flexibility was not known. My hard lesson taught me several things; have a real experienced installer check out the plan on site, ALIGN all the holes as best you can, keep the PEX warm, don't attempt to exceed the bending radius, and only invite your friends and neighbors when you are certain about the installation.