How to Build a Trailer Hitch Lock

1). Measure the width of your trailer hitch and trailer attachment arm when connected. Measure from one side of the connected pieces to the other. Determine the diameter of the lock holes on the hitch by using the measuring tape going from one side of the circle to the other. Common sizes are 1/2 inch to 3/4 inch.
2). Place a metal rod -- either 1/2 or 3/4 inch depending on your trailer hitch hole -- into the bench vise lengthwise. Tighten down the vise and measure the length of your hitch width plus tow inches along the bar. Using the hacksaw, cut the measured bar piece out.
3). Place the sawed trailer hitch lock bar back into the vise lengthwise. At the end of one side, 1 inch from the end, mark a dot on the bar. Use this as a reference to drill out a hole for the padlock arm. Place a 1/3 inch bit into the drill and drill the hole going straight through the bar.
4). File the drill ends to make them smooth. Pour some dry graphite lubricant into the hole. Drill another hole 1 inch from the end on the opposite side of the bar and file and lubricate.
5). Insert the bar into the trailer hitch hole when the trailer is attached. Place one padlock into each hole and lock.