I think it is a 1/4 inch male tab (or disconnect), similar to those shown on page 121 of the following: http://multimedia.3m.com/mws/media/592240O/03-termnl-kitstools-vemd-2009-catalog.pdf
Not that I'm an expert like most of the others here, but when I installed the bus wires and droppers, I did the following.
I ran two 12 gauge bus wires (+/-) in parallel around the layout. I then used suitcase connectors to pull off a short 12 gauge feeder to a terminal block. I then connected 22 awg feeders to the terminal blocks and soldered them to the tracks. I haven't had to do it yet, but it allows me to easily disconnect the rail feeders from power if need be.
I sure others would do it differently, but this worked at our house.
GauchoEvery connection adds resistance and it maybe a point of failure.
I hear you, but I only ran about 20-25 feet of bus wire in total.
Posi-taps are the way to go, can be bought in bulk and are reusable, over and over again.
Solder works on all wire sizes.