These are fine. You need 2 pairs for the Ford 6000CD. Important to insert them so that the curved sides of the blades (with the notches) face towards the centreline of the radio. They should 'click' when engaged, then push the left pair to the left and the right pair to the right and the radio should be able to be pulled put. It's best to take the keys out before sliding the radio back in, because they tend to jam in the catches. And make sure that the aerial is plugged in properly, it unplugs rather easily.
It you stick the keys in the wrong way round they will definitely jam.
This superb little YouTube clip show exactly how the clip mechanism and key works (when the clip is depressed, the radio can slide out):