Speedo woes. Series 3 Sil front hub.

My old speedo was too old I bought a copy reproduction new. The lower inner cable fits fine in the drive at the wheel, the outer fits correctly at the wheel. At the other end the outer fits the new speedo correctly, but the inner is too small and spins round inside the speedo. I have read about the different threads on cables but not the inner at the speedo. Can anyone throw some light on this please.
Colin
Colin