So this set is a 5.3" + 3.35" sized twin plus one you could stick under any twin plus trailer-ready bottom, but it'll also surely liven and loosen up any regular tri-finned board you're surfing now. Two sturdy upright twins with a nifty little trailer fin will speed up you're board and make it easier to turn because of the smaller center fin and smaller rake of the side fins without losing any stability whatsoever. Enjoy!

Oh and here's the full lingo by Macho:

Mark Richards inspired twin fins + central stabilizer fin.  Get the speed, drive and fun ride you’re looking for on your twin fin or fish, and enjoy a little more control with the addition of the small central stabilizer fin.  This combined with the unique flow of 100% fibreglass fins.