speedo cable length

I am installing a new speedo cable and i am running into a problem. The metal piece that extends out of the cable that goes through the speedo senser is not long enough to go into the speedo gear itself. It is about an inch away from being long enough. my car is a 90 gt, is there anyway i could of gotten the wrong size cable? Thanks in advance for your reply - Jim

its not that the cable is to short, it is the metal piece that extends out of the cable and goes into the speedo sensor and gear. does anyone know what i mean