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 (K), to purchase this motor you must be Tripoli, AMRS or ARA level 2 certified (or attempting a level 2 certification).
K400 Classic DMS™
Motor K400 Manufacturer Aerotech Type Single Use (Disposable Motor System™) Flame Classic Quantity per pack 1 motor Diameter (mm) 54.0 Length (cm) 35.9 Ejection Delay (s) 14 Average Thrust (N) 409.0 Maximum Thrust (N) 546.0 Burn Time (s) 3.2 Total Impulse (Ns) 1304.0 Total Mass (g) 1194 Propellant Mass (g) 493