Improperly mounted couplers wreak havoc on a model railroad. The slightest dip in the track can cause cars with mis-aligned couplers to part, causing run-away trains or stranded cars. Coupler trip pins that hang too low snag track components and cause derailments; pins that are too high will not uncouple properly over track magnets. Our easy-to-use machined aluminum Coupler Gauge checks coupler and trip pin height for conformance to published standards, eliminating the annoyance and embarrassment of derailments and parted trains. Works with all brands of HO standard gauge couplers and Bachmann On30 couplers.