The way I made it was a bit of a trial and error process. The one I have on the boat is actually the fourth ring that I've had on the boat, but it needn't be that way.
We made the rings on the spare peice of aluminium tube from the end of the spinnaker pole. From memory it was easier to get 4m sections from the aluminium manufacturer and we had to cut them down to 3.4m or whatever the measurement is so we had about a 600mm offcut. I know I'm mixing unit measurements but I'm sure you'll understand.. The spinnaker poles were 38mm diameter.
We created the rings in two different manners. Michael put the pole offcut in the vice and then stuck some packing tape on it so that the fibreglass wouldn't stick and then set about attaching the ring.
I decided to cut some sections off the offcut about 8-10cm in length and then bent them out so that they slid over the pole offcut and would slide over the pole as well. The idea being that we could move the ring up and down the pole to find a good place for it before drilling holes and riveting it into place. As it turns out, both systems seemed to work fine. Michael just rivited through the fibreglass into the pole.
Anyway, we got some vacuum tube (which is just ribbed plastic pipe about 40mm diameter available from hardware stores) and made a ring which we thought would do the job and then used some fencing wire to tie it to the pole cutoff. In my case I tied it around the stretched out offcut peices around the offcut.
Then its just a matter of going crazy with the fibreglass
The first one I made was just simply too small - I have no idea what I was thinking but the hole in the middle was only about 18cm wide.
Sure, laugh all you want but I honestly had no idea what I was doing, even if the idea was going to work and be strong enough.
The second one I made (which is probably the most robust to be honest) was much bigger (about 30-32cm hole size) and was made with a twist in it to open the bag up a bit which worked reasonably well but was just the tiniest bit too small. The twist worked well but with a new spinnaker it just didn't really want to all bunch up and suck into the hole all that well.
So I had to make another one. By this time I was wondering if I shouldn't have just spent a whole chunk of money and bought one of the aluminium ring thingys but fibreglass, vacuum tube and tie wire aren't all that expensive so I made number three.
I thought that the Guck snuffer system looked quite good so I made the thrid one bigger (about 35-38cm) and for some reason I made it flat like the Guck one instead of having a twist in it.
Unfortunately this ring had the same problem as the second one. The kite would go through the hole fine bit it also had to open up the bag and turn the corner into the bag as it went so it didn't really work any better than the second one.
This would be why the Guck systems have the fibreglass turn in the bottom of them.
Because the vacuum tube is plastic and smooth, the fibreglass actually doesn't stick to it, it just acts as a backbone. So what I did was to cut the fibreglass with a hacksaw in two places about 45 degrees around the ring and then put a twist in it and glassed it all back up again.
This isn't even making sense to me as I'm writing it but I'll take some photos this weekend and post them up next week and you'll have a better idea of what I mean.
Hope this helps.