This is the Hornby R7399 OO Scale Vacuum Pipe Magnetic Coupling Pack - 20mm

This coupling pack is the perfect accessory for the Big Four era and BR Mark 1 and 2 coaches. This pack does away with the somewhat intrusive tension lock coupling and replaces them with something that more resembles vacumm pipes as you would see between coaches on the UK mainlines. These couplings also hold the coaches closer together than has previously been possible, again adding to the realism of any coach rake.