Fuel tank gauge sender unit strengthening ring, most Smith's fuel sender units & sump sender units on DB2 & 2/4 are getting a little tired now, 

When you tighten up the 6 screws the face of the sender buckles & it wont seal properly.

This ring fits over the main outer body & sandwiches the fastening ring of the sender between the tank or the sump, its held by the 6 screws. & helps keep the (rare) sender unit flat & stop the face buckling & then leaking, our plate easy to fit, plated for long life & anti- corrosion.