The Swindon Class 126 DMU's were equipped with two types of coupling, these being screw couplers (coupling hooks attached to fronts of vehicles and coupled together via a coupling chain/link) and also American style knuckle couplers called 'buckeye's'. The Knuckle head could be raised and lowered. With the knuckle in the 'raised' position the standard screw couplers could not be used as the knuckle head covered the drawhook but with the knuckle in the 'lowered' position which cleared the hook, screw coupling could be used but 'Buckeye' could not.
This shot of the lower front end of DMBSL 51043 as it stands at Birkhill on the Bo'Ness & Kinneil railway service during the diesel gala event on Saturday 4th September 1999 shows the Buckeye 'knuckle' coupler in the raised position. Also note a Freightliner taillamp being used.!!!

Photo and Scan: Ross Aitken (aos@cableinet.co.uk)
Website: http://wkweb4.cableinet.co.uk/aos/photography