TP,
AWS D1.1:2006 Figures 4.1, and 4.2 show the positions for groove welds and fillet welds.
Figures 4.3 and 4.4 show the testing postions for plate and pipe groove welds.
Figures 4.5 and 4.6 show the testing postions for plate and pipe fillet welds.
1G=flat groove weld
2G=horizontal groove weld
3G=vertical groove weld
4G=overhead groove weld
5G=groove weld on pipe or tube horizontally fixed and not rotated during welding and requires welding flat, vertical, and overhead.
6G=groove weld on pipe in a 45* fixed inclination and not rotated during welding.
6GR=groove weld on pipe in a 45* fixed inclination with a restrictor ring to act as an obstacle and the pipe is not rotated during welding.
1F - 5F is basically(not exactly) the same as the groove welds but only requires placing a fillet weld.
There is no 6F.
Hope this helps,