A scratching surface and a piece of furniture can share the same object. Begin by looking at how the surface is made.
Wrapped rope
Our sisal wheels, balls and posts use rope around a form. A wheel, upright post and flat mat offer different shapes; the surface alone does not tell you the size or how the piece is supported.
Layered board
Corrugated scratching surfaces appear in cat dens and sofas. The shell and scratching surface may use different materials, so check both. Selected house designs are listed with removable cores.
Before choosing
Compare the footprint, usable surface and opening of the exact option. Check what is included: a replacement ball or cover is different from a complete piece.