This is a 54mm diameter single use motor. It is ready to fly and doesn't need any motor hardware. You will still need a retaining system.
Because of the impulse class (J), to purchase this motor you must be Tripoli, AMRS or ARA level 2 certified (or attempting a level 2 certification).
J250 White Lightning™ DMS™
Motor J250 Manufacturer Aerotech Type Single Use (Disposable Motor System™) Flame White Lightning™ (W) Quantity per pack 1 motor Diameter (mm) 54.0 Length (cm) 21.8 Ejection Delay (s) 14 Average Thrust (N) 260.0 Maximum Thrust (N) 338.0 Burn Time (s) 2.7 Total Impulse (Ns) 704 Total Mass (g) 708 Propellant Mass (g) 363