The SR side fins are based on the pre twisted Witchcraft side fins. They come in pairs of 11.5 (for quads or small tri fins), 12.5 (for bigger quads or medium sized tri fins) or 13.5 for bigger tri fins/thrusters.
These fins do not increase drag and give more drive so you can use bigger side fins and a smaller trailing fin(s). Especially on tri fins you can use 3 more equal sized fins, for example we replaced the original 19cm centre fin plus 11cm side fins on a Quatro Pyramid 96 for 13.5 SR side fins with a 14cm Witchcraft centre fin. This dramatically improves turning, drive, speed, control and up wind ability. But also on other trifin boards like free wave board or quads they improve performance. Ideally combined with Witchcraft trailing fins so the fins all work together optimally.
They do not work on Witchcraft boards as there will be too much toe-in.
See for more information on the working: https://witchcraft.nu/boards/trifin/ or here: https://witchcraft.nu/windsurfing-science-witchcrafts-bouke-becker-answers-the-question-what-is-drive/
Material: Orange G10