First step in converting these calamari rings is to remove about ¼ to 1/3 inch from the circumference -- basically putting a gap in the calamari.

You can do this several ways. With a hacksaw you can put the rings on some sort of sacrificial mandrel (bamboo or even pvc) and saw the sections out , or you can warm the pvc with a torch even boiling water then you can use a box cutter or those EMT rescue scissors do a good job.

To avoid future unwanted sharp edges: Using nippers, scissors, box cutter or even sanding block, bite the sharp corners of the gap.

At this point you have a great spar clip. 5 or 6 of these will hold a tarp sail to a bamboo or pool skimmer handle spar quite nicely.

The next step is bending the PVC. This can be done with a vise, big electrical pliers, several, smaller pliers, even a ball peen hammer and a hard surface. 

I have found a roofer’s hand seam clamping lever action tool to be a very useful canoe sailor’s tool as a hand vise and does this job wonderfully.

Warming the pvc helps avoid cracking – leaving it out in the sun may be good enough.