So did you measure the hole between the threads, or were you guestimating the outside edge of the threads? I suspect you measured the hole, which would probably make it a 3/4" thread. Then its either fine thread, or course thread, but its probably fine thread. The next smaller standard bolt size would be a 5/8" either in course or fine thread. An 11/16 is an odd size.

Take the shift handle with you when you go to a real hardware store and check to see if a 3/4" bolt (or a 5/8" bolt) will screw into it, you should be able to look at the threads to determine if you need a fine thread bolt, or a course thread bolt. You may be able to get an insert for that big of a bolt, but it probably won't be in stock. Do not let them sell you a pipe thread reducer, it won't work, the thread count is wrong. You may have to step down one size at a time.

If you know what you need, you might be able to get one from www.mcastercarr.com. Gene