Which Plug for Which Screw?

As a general rule: Yellow plugs fit into 5.0 mm holes and work best with screw sizes 3 and 4, but can be used for screw sizes 3 through 8. Red plugs fit into 6.0 mm holes and work best with screw sizes 6 and 8, but can be used for screw sizes 6 through 10.

What are plugs used for with screws?

A wall plug (UK English), also known as an anchor (US) or "Rawlplug" (UK), is a fibre or plastic (originally wood) insert used to enable the attachment of a screw in material that is porous or brittle or that would otherwise not support the weight of the object attached with the screw.

Do you use the same size drill bit as the screw?

The drill bit should be the same size as the shaft of the screw without accounting for the threads. To do this, simply line up a screw side by side with the drill bit. If they're the same size, then you're good to go. You can also look for the measurements labeled on most bits and screws.