The recommended minimum radius curve in 7mm scale is 4ft. For operation down to 3ft radius, use the MP7 mounting plates. They also have the added advantage of making the couplings easier to fit.
To fit and make the couplings fully operational, you will also require NSW7 nickel silver wire, SIW7 soft iron wire, and permanent (7MAG) or electromagnets (PK MAG). Alternatively, you could just purchase the S/AC7/3 starter pack, which contains the fret, the wires and two permanent magnets. A cheaper trial pack (T/AC7/3) is also available, with eight couplings and mounting plates, wires and one permanent magnet.
The actual size of the fret is 103½ x 138½mm; it is etched in 0.018″ brass. Each coupling is 42mm long and 12½mm wide.