Part number 90-423-7127 (also cross-referenced as O-629 or AS568 #127) is a generic Buna-N O-ring with a 1-7/16" inner diameter and 3/32" cross-section.
In the hot tub industry, this specific O-ring is primarily used as a seal for high-flow valve assemblies, specifically the Waterway Top Access 2-way and 3-way Diverter Valves and the Balboa Water Group (HydroAir) Hydroflow 3-Way Valves.
Hot tub manufacturers that utilize these specific valve components—and thus use this part—include:
Artesian Spas: Uses the Waterway top access diverter valves that require this seal.
Cal Spas: Frequently incorporates Waterway diverter valve assemblies.
Clearwater Spas: Identified as a brand using these specific valve parts.
Master Spas: Uses this O-ring size (sometimes cross-referenced as internal part X804184) for their valve components.