In article , YAPH wrote:
On Mon, 17 Nov 2008 12:20:21 +0000, Doctor Drivel wrote:

The snips the makers provide to cut plastic pipes don't help as they
leave a proud sharp point that can nip the O ring.

Fitting an insert as per the mfr's instructions effectively gives the cut
end a chamfer, protecting the O-ring from the square edge.

The instructions I've seen only want inserts for compression fittings,
for example when joining to copper. And not all insert types give a
chamfer, even if you used them on other joints.