Hi, Sorry for the delay in responding. I am busy getting prepared for the PACCIN workshop to be held in San Francisco in collaboration with AIC and their annual meeting later this month. Can you open the image that oner0002 includes in his post? If so I would consider sending that to the manufacturer. If you want to find specs from the post that I forwarded from the listserve you could go back and find the original poster by searching the Archive. The main thing that I would say is that be sure to have them made long enough to give you room between the screen and the painting so they will attach easily. The picture indicates it is about four inches long with an opening of an inch or so. I would have mine made at least that long but maybe with the hook opening slightly smaller if possible.
If you want more input you could also post your inquiry directly on the PACCIN listserve which goes right into the mail box of a bunch of knowledgeable folks. To sign up go to this address http://www.paccin.org/content.php?110-ListServe
Another option is to set up a bending jig and make them in house. I used to do that using locally purchased brazing rod back in the day...
Good luck!