Doug Fattic 

I use 1/16" 56% silver when brazing lugs because it is conveniently available. Whether smaller diameter wire works as well depends on the coordination of the person brazing. Some decent percentage of my frame building class students have trouble having their hands do different motions at the same time. If they are moving the flame with their right hand, their left hand freezes and if they are moving their left hand to keep the silver in the right place as it melts, their right hand with the flame freezes (assuming they are right handed). The most successful brazers can move their hands independent of each other. So because smaller diameter silver requires more hand motion to keep the silver in the right place, it creates more problems for people with average or less hand coordination.

Here is an exercise to try to see how independent your hands can move. It is similar to pat your head while making circles around your tummy. Point a finger from your left and right hand towards each other. Now make a circle with one finger around the other. Once you get that circle started, do a circle in the opposite direction with the other finger. 90% of people can't do this at 1st. The 2 fingers will go in the same direction like pursuit cyclists on a track. If and when they can go in different directions their circles will be more like ovals. Try it and see. This lack of independent hand motion is at the foundation of problems learning to braze.