A shade carrier (also known as a gimbal or gimble) is an adapter used to connect a lampshade with a duplex fitting to a lamp holder. There will be a bit that screws off below the light bulb to hold it in place.  The duplex ring of the lampshade then sits comfortably on top of the shade carrier, but the lampshade can easily removed for cleaning or moving.
This shade carrier will fit a standard 29mm UK bulb holder and 11cm/4 1/4” approx. duplex ring.
It has a pewter/matt metallic powder coated finish (as opposed to standard white) which will team well with any bulb holder be it gold, nickel, white or black and especially compliments aged/antique gold lamps and fittings .
The size for a shade carrier can be determined by placing your shade on a flat surface and measure from the inner ring down to the flat surface then minus about 2 1/2"/6cm to find the approximate height of the shade carrier that I would recommend.
Generally:
For a small/medium table lampshade I would recommend a 4" to 6” gimble
For a large table lamp/small standard lampshade or dome shaped lampshadeI would recommend a 6" gimble.
For a larger standard lampshade (tall 18" or 22" shade) Iwould recommend an 8" gimble depending on your base style.