D-rings are almost universally used in trailers with wooden floors, because their design requires that a hole -- properly called a rebate --- be made in the substrate to accommodate the sunken area in the D-ring plate. The sunken area exists so the D-ring itself is flush with the floor when not in use.
Determine the best location for the D-ring as dictated by the load it will be supporting or protecting from theft; load your motorcycle and determine the position so that the chains that are to be used will be as close to 45 degrees off horizontal as possible.
Use an electric drill to make a shallow rebate to accommodate the sunken area of the D-ring. The manufacturer's instructions invariably state what size wood-boring bit must be used to cut this rebate; typically a 3-1/2-inch bit is used for 5,000-lb. units.
Insert the D-ring into the rebate and align it as required; tie-downs have more strength when the D-ring is aligned with its hinge toward the point of strain. Use a permanent marker pen to mark the locations of the four holes through which the fasteners will pass.
Check beneath the floor to confirm that no wires or brake lines pass immediately beneath the location of the D-ring; if they do, release them from their securing devices and move them temporarily. Use the electric drill with a bit sized to the fasteners to make holes through the trailer floor where each of the marks are.
Put the D-ring in place and thread the fasteners through all the holes. If no fasteners were provided, use heavy-duty Grade 8 nut/bolt/washer assemblies. Anchor bolts with recessed heads make it harder for potential thieves to remove the D-ring and steal it and the chains along with the motorcycle. Go beneath the trailer and fit the washers and nuts. Some D-rings are supplied with a steel backing plate rather than washers; follow the manufacturer's instructions to ensure the D-ring is properly reinforced. Tighten the nuts using a wrench or socket set.
Re-secure any wiring or brake lines if necessary.
