Does anybody know the plug gap for a RCT2800B Ryobi streamer

you should be Googling this yourself, check the model number on the spark plug then google the spec or "spark gap".... that would've been quicker than asking this question.

.025" gap

No need to gap from a new spark plug unless the plug was dropped on the electrode.

Hi and welcome to FixYa, I am Kelly.
The spark Plug Gap is 0.030. Any original or aftermarket spark plug for this unit is pre-set to 0.030. Unless you dropped the replacement plug it should be fine. All Ryobi engines 2 and 4 cycle have a 0.030 spark plug gap.
Thanks for choosing FixYa,
Kelly

The correct gap according to my RY64400 operators manual is .025 and the torque is 170-190 inch lbs. The spark plug is NGK CMR7A or Champion RZ7C.

The gap for the Weed Eater 20cc engine can be set @ .025". The larger engine Ryobi 31cc/32cc class can be set @ .030" Either engine would operate within that .005" range and I know a 32cc Poulan calls for a .030" gap.

close your carb adjustment screw a bunch of turns... yours may even be missing.

Ryobi RY60511A
Champion plug RCJ6Y - gap is .22
I have original manual.

0.54 is the gap for the plugs