The difference is in the top rail profile. Both AFCO 175 and AFCO 275 use AFCO's metal railings with steel cables for infill. AFCO 175 Series uses a rounded top rail, which you can find above as AFCO Pro. AFCO 275 Series uses the Flat Top rail shown above.
AFCO Pro Horizontal Cable Railing

A beautifully-designed railing with amazing views. AFCO Pro Cable Railing makes it easy to enjoy your deck, from the stylish, crafted railing design to the amazing way the stainless steel cable disappears into your gorgeous deck view.
No one beats our in-stock selection of AFCO Pro Cable. Customize your top rail and get all the bracketry you need in one place. DecksDirect carries the most options and our project planners help you personalize your railing!