3/8" A36 steel. Targets L to R 12", 9", 6", 5" 4", & 3". I use the 12", 9", & 6" at 200yds; 6", 5", & 4" at 150yds; and 5", 4", & 3" at 100yds.
As a MD you can do a "know your limits" type stage or you can do a set point value for each target size with say 5 shots. We had a local centerfire match do the latter version of the stage at 600yds with IIRC a 12", 8", and 6" circle; point values of 10, 20, & 40. You saw a lot of different strategies employed, though only a few successfully.