Splashers, for those unfamiliar with the term, are die and hub trials which are usually uniface (one-sided) to test the progress of a design or concept. They are usually struck in soft metals such as tin or lead. Some are even known struck on non-metallic materials such as cardboard or wax.
They are found in Appendix A in the Judd book and are listed by Pollock under the 3000 number series for mint products, 5000 for private pieces and the 6000 number series for one sided pieces struck outside the mint from dies sold as scrap. This site lists them by both their Pollock and Judd 9th edition numbers.