There is no definitive answer to this question as the size of split ring needed for a Tokyo Rig will vary depending on the fish species you are targeting, the size of your lure, and the conditions in which you are fishing. However, a good rule of thumb is to use a split ring that is approximately one-third the size of your lure. For example, if you are using a 3 lure, then a 1 split ring would be appropriate. If you are fishing in heavy cover or with large fish, then you may want to go up to a larger split ring size.