There are different 3-pad layouts, so I’ve been referring to the standard one as Gchart’s 3-pad layout, since he came up with it. The layout is + - R with a 1.27mm (50mil) pitch.
I also sell an USB-UPDI adapter for drivers using Gchart’s layout, mainly for people outside the US since shipping costs less for me, well except that I’m out of stock at the moment 
There is also AVRDUDESS, a GUI for AVRDUDE, and ZflasherAVR for Android that people tend to prefer using over command line software.