The part number 48-260050-13A refers to a 5.5kW flow-through heater assembly made by Hydro Quip, which is used in hot tubs from several manufacturers, most notably Baja Spas.
The following manufacturers use this specific part in their spas or as a replacement for their control systems:
Spa Manufacturers
Baja Spas: This specific model is a known replacement heater for Baja Spas hot tubs.
Various other brands: Because the control is an aftermarket or universal-style replacement, it can be found in other brands that use Hydro Quip control systems, though specific models are less defined in general listings.
Component Suppliers
Hydro Quip: This company is the original equipment manufacturer (OEM) for the 48-260050-13A heater assembly.