22mm x 3/4 inch solder ring coupler.
New metric 22mm tube one side, old (pre 1972) imperial 3/4 inch pipe in the other.
Only suits the old British imperial pipe (other countries, like Ireland and America are different).
Pre-soldered capillary plumbing fitting for copper pipe, made to the European standard EN1254.
Fitting contains the correct amount of solder for a perfect joint, though you need to use flux (we keep this in our store).