Anything ego or 510 threaded will fit. With 510 threaded toppers, you may want to use the beauty ring or a separate flared cone to dress it out.
Lot's of choices in toppers. Pyrex ones, like the Kanger PT2, that use single bottom coils can be rebuilt with better wicks and coils. Dual coils - more vapor, use more
juice, and rebuilding is a maybe thing. Pyrex lets you not worry about the
tank being destroyed by some flavors.
Or even something like a Kayfun on top will work, but you need to have the materials to build coils, wicks, and be sure to check the ohms before firing!