Just gone to fit my new distributor cap and rotor arm on the Astra and the rotor arm doesnt seem to fit

The original cap that came off was a Bosch (Light brown) and the motorfactors swear that they've given me the right rotor arm but the middle of it is too narrow to fit on the bit that sticks out.

Any gen peeps ? Unipart are being pretty good trying to work out what is what but if any of you know for certain what type of system it is then it would be appreciated.

The car is a 1994 1.4 Spi (60Bhp) High Torque Astra Merit.