4 Hornby X6354 NEM pockets to suit all OO rolling stock with a dovetail mount. They fit other brands such as Bachmann & Dapol as well.  These are genuine Hornby products, but in some models they may be a little loose in the dovetail cutout.  If this is the case just use a little bit of blue tack, black tack or a tiny drop of super glue.  If using super glue, just check that there will be no need to remove the socket later. 

The last picture shows other the coupling styles that I usually have in stock.  Search my other listings for the ones you want.