Available from Finney and Smith-see link, this particular set can be used for 'n' Gauge up to '0' Gauge (Just). The basic set comprises of three saddles designed to attach between the rails of your chosen track- I have made a couple of plinths, one with 12mm track and the other with 16.5mm 00 gauge track.
The saddles come with a designated allen key and a couple of spare grub screws. Simplicity itself to install and use, the lower photo shows a Pannier being run in, I can keep an eye on it should it stall whilst running in front of me on the workbench. Highly Recommended!