I've heard that making a mizrab is hard to do. I have big hands too, so I use the largest size I can find but still have it fit tight so its doesn't wobble.
The gauge of the steel, plus distance from the middle of the joint to about a quarter inch beyond the fingertip are two things that are important. Look on Lar's site sitarsetc.com under mizrabs. He gives a pretty good explaination of how mizrabs are fashioned, plus the various sizes.
Hi Paul, It's difficult to make mizrabs, I have tried with even a light gauge wire (about 1/2 the size thickness of the mizrabs I get), didn't have much luck. There is a diagram in the book "The Sitar" by Manfred Junius showing how they're made. If you need a nice custom fitted mizrab, I have them and pick them out according to your finger measurments so there's little if any guesswork. But if you have some #7 to #9 piano wire laying around then give it a try.....!