My Speedo cable has stopped turning, I’m guessing the cable has snapped and it’s nothing more serious, does anyone know if a standard Sierra cable will fit it? I have a type 9 gearbox and tigers mechanical Speedo

More likely to be the square end gone round.
Yes Sierra will fir

I would be checking the speedo drive in the box is turning.
I had the odd situation where the speedo drive gear on the output shaft slipped and so that did 2 things. Firstly no drive, secondly stripped the plastic drivegear. Solved by some bearing lock andmanaging to slide the gear back, and a spare plastic drive. Worth a check while you are in there.