The B66/B67 series is the most popular of Brooks's sprung models. They are an excellent choice for recreational or utility cycling in a fairly upright posture. The B66 is most appropriate for cyclists who set their handlebars higher than their saddles.
In general, the more upright your riding posture, the wider, and more heavily sprung, the saddle you should choose.
These use a special clamp (included) for old-style "pipe-type" seatposts.
To use them with modern "microadjusting" seatposts,
you need a "Seat Sandwich" (See Related Items).