The grit of sandpaper you should use for wood depends on the type of project you are working on and the condition of the wood. Here are some general guidelines based on the search results:

• Coarse grit (36 to 80): This grit is best for fast stock removal, such as smoothing the live edge of a slab or sanding down rough-sawn surfaces.

• Medium grit (100 to 180): This grit will remove any mill marks from your machines and give you a generally clean and clear surface. Some finishes will recommend only sanding up to 180 to allow the finish to “bite” onto the surface of the wood.

• Fine grit (220 to 400): This grit is generally used for sanding smooth surfaces or preparing wood for finishing. Its also used for sanding between coats of finish and for distressing.

• Extra fine grit (600 and up): These grits are used for polishing finished surfaces and are only occasionally employed in the wood shop.

When sanding bare wood, its recommended to start with the finest grit of sandpaper that allows you to get the job done effectively. For heavy sanding and stripping, you need coarse sandpaper measuring 40 to 60 grit; for smoothing surfaces and removing small imperfections, choose 80 to 120 grit sandpaper. For finishing surfaces smoothly, use extra fine sandpaper with 360 to 400 grit.

Different types of wood require different grits of sandpaper. For example, for open-grain woods (such as Oak, Ash, Mahogany, Parawood) that will be stained with water-based products, use 120-grit, followed by 150-grit, then 180-grit. For closed-grain woods (such as Cherry, Pine, Maple, Birch or Alder) that will be stained with water-based products, use 150-grit followed by 220-grit.

When using sandpaper, make sure you always keep the pressure even so that your finish stays nice and level. You also want to make sure you sand with the grain of the wood, so you do not cause any unnecessary scratches or imperfections.