The reason you would use a grade 80 screen is to remove the grade 100 hardplate scratches.
How to use floor grit pads.
Choose coarse grit sandpaper in the 40 to 60 grit range for basic sanding and stripping.
Swirl marks in the wood or if the finish has worn down to the wood in certain areas.
We generally use this grit when first smoothing pine redwood cedar.
By the time you are done there shouldn t be any old stain left on the floor.
For the smoothest finish use superfine sandpaper 200 to 400 grit or higher.
You can hand sand corners with 100 grit to blend.
You typically would follow that by hardplating with 100 grit abrasive paper.
Next you would use a grade 80 screen backed by a red pad then a grade 100 screen with a white driving pad.
The only exception would be a clear satin finish in which case you may want to eliminate any scratches left on the wood with p150 or p180.
Remember there is two sides to a screen so flip mid way through and use more than one screen for a larger area.
You will want to use this coarse paper to go right down to the original floor.
For smooth finishes and removing minor imperfections use 80 to 120 grit sandpaper.
Use 24 grit sandpaper if there are sander flaws e g.
Lastly enamel paints and polyurethane don t require the wood to be sanded beyond p120.
If you use a wet dry sandpaper you can wet the area before you work to keep dust down.
From here you will want to sand the floor with a 60 grit paper a 100 grit paper and possibly a 120 grit to get a really nice smooth finish.