The part number 25591-210-000 is a Custom Molded Products (CMP) Spa Master 3-3/8" Scalloped Directional Jet Internal.
CMP is a major OEM supplier, so this non-proprietary jet is used by many hot tub manufacturers.
While specific usage can vary by model and year, this generic jet internal has been used by or is compatible with spas from the following manufacturers:
Artesian Spas
Beachcomber Spas (pre-2001 models often used a similar Waterway version)
Bullfrog Spas
Cal Spas
Catalina Spas
Clearwater Spas
Coast Spas
Coleman Spas / Maax Spas
Dynasty Spas
Great Lakes Spas
Marquis Spas
Master Spas
Platinum Spas
Strong Spas (on some models using Waterway/CMP components)
Sundance Spas
Vita Spa
Zodiac Pool Systems (uses this part in some gunite/fiberglass pool jet applications)
Jet Specifications
According to merchants like Pool Warehouse, the jet has the following specifications:
Face Diameter: 3-3/8"
Style: Deluxe Scalloped
Internal Type: Directional internal with adjustable on/off control
Installation: Thread-in style
Color: White (the -210 in the part number denotes this color)
Because many manufacturers use standard "open-source" parts from suppliers like CMP and Waterway, this jet may be compatible with many other brands not explicitly listed here.