Is the 'sleeve' on this large enough to fit over a 1/2" pvc pipe?
NO, sleeve is too small. Go to Home Depot or Lowes and get a hard plastic dowell. I don't think they sell just the dowell, so you'll have to buy the reflective attachment with it. It is originally designed to mark a driveway or entrance, and costs about $5.00.
If you already have the 1/2" PVC pipe mounted to your boat, you could then cement the dowell in the PVC pipe.
To get extra height, I slid the PVC pipe over an old and unused ship-to-shore radio antenna. The antenna is mounted where it can be lowered, making it easier to remove the flag.
I use it on my UHF antenna on my boat which is put up for the winter but I think 1/2" will work. It's an outstanding flag but I can't put my hands on it to tell you for sure. I have to use a bungie on it to keep it from coming off in high winds or surf but if it does not fit it has holes for zip ties to attach it to just about anything.
The flag is packed away for the winter, but if memory serves me, I think the sleeve is probably too small for 1/2" PVC.
No it did not work on the one I have. 1/2' pvc is around 3/4" outside diameter, also the two grommets also take up space on the sleeve.
Unfortunately not as configured. The sleeve does appear big enough, but there are two gromets, one at the base that is key to the support wire stiffner which blocks the full circumference of the sleeve...you can see it in the picture, it is punched right on the seam and takes up more than half the sleeve.
I do not believe it is large enough, even so the metal brads would prevent it being slipped over