That's normally called a Balanced Action or BA. The best alto I ever played was a BA that was on consignment at Barnard Repair and in need of an overhaul. I still kick myself for not buying it.
You can check out this video:
Repairman's Quick Overview: Selmer Balanced Action Alto & Tenor Saxophones
You can check out this video:
Repairman's Quick Overview: Selmer Balanced Action Alto & Tenor Saxophones
