So i bought this parker (and a pilot short pen 2) on a whim because it was so inexpensive about $17 for the both of them. Now when i got the pen i was puzzled with the parker because in the cap it stated that it was a parker 21 but when i unscrewed the body i was shocked to see that it came with the standard 51 aerometric sac. The body didnt have any indication that it was a 51... I havent been able to take it apart since i left it at my dorm and im currently out of town, can anyone help me identify it?