The Cat7a specification refers to ‘Category 7 augmented’, or Class F Augmented products. This was introduced by ISO 11801 Edition 2 Amendment 2 (2010), and is defined at frequencies up to 1000 MHz.
Category 7a cable was likely originally introduced as a future-proofing step for the anticipated wider uptake of a 40 Gbps Ethernet standard - however, in 2016 a new ratification meant that this responsibility was effectively handed over to Cat8 cables specified to 2000 MHz. As a result, cable Cat7a as a standalone revision isn’t officially supported by very much equipment to run at significantly faster speeds than Cat7 versions, although speed boosts may be possible in certain applications.
Cat7a Ethernet cable is generally slightly thicker, due to additional shielding intended to boost it towards delivering 1000 MHz speeds. Even so, Cat7a is not technically recognised as a wholly separate revision by most standards today, most notably by the US Telecommunications Industry Association (TIA).
Rather, it’s generally considered alongside Cat7 for performing at similar speeds and distances in most day-to-day applications and environments. Either standard would be seen as a suitable option for demanding use scenarios, such as high-performance data centre applications.