Best lock for trailer to ball hitch?

I placed my lock on the trailer this morning and forgot to hook it up. I lost the lock somewhere between home and lake fork. I need to replace that lock, which makes me wonder what is the best theft resistant lock for the trailer that attaches to the ball receiver?

The receiver is the square hole on your truck into which you insert a ball mount. Are you talking about a locking pin that goes through that? Or, are you asking about a lock for the trailer coupler (which is the nose of the trailer that goes over the ball?

For couplers that simply have a narrow latch on top, Materlock makes a very beefed up padlock with a shackle shroud that greatly impedes cutting the lock off.

For the most common square-end bass boat surge brake actuator (UFP A-60), I like and use a lock such as this by Deadbolt:

Wide Deadbolt Lock

I am looking for a lock for the trailer, not the receiver. The link that you provided is exactly what I am looking for. Thanks.

You can take the lock above and a 2" ball. Cut the shank off the ball, When you unhook from the truck place the modified ball into hitch of the trailer and place the lock on.

I haven't tried it, but I'm wondering if the coupler adjustment nut will back off enough to let that ball drop out of the coupler, thereby letting a thief lower it onto their own ball? I ask because I once towed someone else's trailer that had never had the nut tightened, and while towing, the latched coupler lifted off the ball!

For when I am unhitched, I have another lock mechanism that I use; it has a U-bolt over the coupler that locks into a platform with a faux ball on it. This locks around the coupler, slowing down a thief intent on stealing it.

Yes, the hitch can be taken off by loosening the adjustment. I once had my wife take my boat to a shop and I forgot to give her the key. The backed off the nut and got the trailer off her truck.

My coupler is the square type it is not the one with an adjustment knob. Didn't know the adjustment type was what he had,

I use a pair of these. One for the receiver hitch and one for the the trailer coupler to the ball. Amazing how many people lock their trailer coupler but not the hitch to the receiver. Not real hard to pull that hitch pin and then steal your motor, boat, trailer AND hitch! In the end the object is to attempt to make it time consuming and difficult enough that a thief simply moves along! :-) :-(

My adjustable solid-billet milled-aluminum ball mount was $300, so you betcha it's got a lock on it! I use a lot of locks and security cables. So far either I've been very lucky, or my stuff was just too much trouble for a thief to bother with because of all those locks & cables. My swing-tongue lock key also fits the heavy duty coated security cable that secures my spare to the trailer frame (not just the tire mount). I noted long ago that every spare I heard of being stolen was unsecured, hence the cable. I've heard of swing-tongue pins being taken possibly as a mischief action, so I tried to nip that one too.

The straight hitch lock ( like linked above) is a joke. I argued with my partner about mine and he showed me real quick that it was a joke. In sandals, he stepped on it and snapped it off. I now use a small short shank master lock that is too tight to cut with bolt cutters and will not impair the swing of the hitch on the ball. Best thing I have found IMO. Truth is, if they want it bad enough they will take it. Neighbors boat in college was stolen with a lock in the hitch. they sat it on the bumper, come-a-longed it to both corners of the bumper and drove away!