CURT Right-Angle Trailer Coupler Lock, 1/4-Inch Pin Diameter, Up to 3-Inch Span Model 23503CURT Right Angle Trailer Coupler Lock, 1 4 Inch Pin Diameter, Up to 3 Inch Span Model 23503 Sometimes a safety pin and coupler latch are just not enough to keep your toys safe. While CURT safety pins and coupler latches are made to keep your coupler securely latched onto your trailer ball, they are no substitute for the locking power provided by a CURT coupler lock. CURT coupler locks are designed to add security to your trailer and towing equipment.