To keep sanpaper discs from curling up, make a simple jig to keep them flat. Cut out two pieces of 1/4-in. plywood that are slightly larger than the discs. Drill a 1/4-in. hole through the center of each of the pieces. Insert a bolt through one piece, lay the discs on it, and follow up with the second piece. Fasten the stack with a 1/4-in. bolt and wingnut.
Ratchets have a square shaft that holds the socket. The size of this shaft determines the drive size. Heavy-duty automotive work generally requires the strength of a 1/2-in. drive tool which has a longer, thicker handle to provide maximum leverage. A 3/8-in. ratchet is a good all-round size. 1/4-in. ratchets are smaller and ideal for lighter tasks in tighter work areas. Drive adaptors are available that convert sockets from one drive size to another. You should avoid using a small socket on a 1/2-in. drive ratchet, because the excess torque can damage the smaller tool.