Retracted gap has the ground wire BELOW the shell of the plug. I have no idea what they were originally designed for, but I do know that some 2 strokes used them. When you have the plug very close to the piston, and you can't index enough clearance, you use a retracted plug. I still have a gapping tool for retracted gap plugs.
One of the issues is when the ground wire is down in the plug shell, they are usually very cold plugs. There is no room to make the shell longer.
What jpar is using is a cut back ground wire plug. There is also surface gap, angle gap, fine wire.
Like I said, getting the correct STYLE plug is first order, then the correct heat range. The ground wire is for picking the fly poop out of the pepper. There are many ways to get quicker time slips for way less work that dealing with spark plug ground electrodes.
