Most trailer manufacturers have data online for gear they sell and it is likely attainable by the reviewing the model's information. What make & model did you acquire?. Additionally, I'll second the recommendation of the Gorilla hitch lock.
I bought a used one off of a friend. Not sure of the model number or make...I only looked it over to see what it needed.
As for the lock, YES!
I bought a puck-style door-latch lock, locks for the coupler and the hitch mount, a lock for the coupler when it NOT in use...
and I bought a wheel/tire boot to put on it when it's parked.
Not to mention new wheels/tires and a whole new light package.
I just need a day at his house to put on the lights and the tires, then a trip to the notary to make it legal.
(once I buy the correct hitch ball)