Solid deterrence for your trailer with locks that secure the coupler or the set screw on the gooseneck. Couplers vary, so a quick flange-width check helps: some locks fit 4-1/2 inches between tabs while others fit 5 inches. For outdoor use, pick a weatherproof padlock and confirm it will fit thru the hole on the locking rod. Expect a snug fit on some couplers and a looser fit on others.
Often yes. Some locks are only for Bulldog couplers, and RAM couplers use RAM-specific locks. Demco EZ Latch couplers use a Demco lock. Confirm the brand on your coupler before choosing to avoid a poor fit or a lock that won't install.
Measure the coupler's flange width. Visual differences are subtle, but flange width decides the fit. Locks for Bulldog/Stallion/Superior/T.E.M. use a width between the tabs of 4-1/2 inches, while RAM-style locks fit 5 inches. Check your coupler for labels or numbers, then match the lock to your measurement.
Use a set screw lock for the gooseneck coupler's height adjustment if a bottom coupler lock won't work with the handle. This secures the set screw to help deter tampering. If your coupler has a handle, confirm whether a bottom lock is offered for that design; some do not have a compatible option.
A slightly loose fit can still impede theft, but verify brand compatibility and flange width first. Some couplers had interference and only installed when rotated 180 degrees, which felt sloppy. Certain Bulldog styles did not fit at all with a given lock, so double-check your exact coupler style before buying.
Make sure your padlock is weatherproof and that its shackle or pin fits through the hole on the locking rod. Confirm clearance for your padlock—some needed to bend flanges inward with a vise to fit a Trimax padlock, while other brands did not need modification. If clearance is tight, try a different padlock that fits cleanly.