Pictured above: This style D tuners was first made by Johnny Whisnut in 1950...then by Henry Lewis, and used by John Hartford...and these pictured have my own improvements....advantages? They can both be used at the same time and they stay in tune...I know, they're ugly...but they work so well it's pathetic. After I found a machinist who knew what he was doing and had them made from steel alloy instead of brass...they work perfectly, the parts do not wear, and they are always in tune. I used this type tuner for the last 7 plus years before the shoulder surgery stopped me from playing...Price? $280 with installation instructions...no drilling...remove nuts from first and fourth tuners, slip the base over them, and tighten them back. Tune it, set 'em...and you're done.