A B737-300 MECHANIC REPLACED THE FIRST OFFICER'S CLOCK WITH A CAPTAIN'S POSITION TYPE CLOCK.

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MET ACFT FOR MAINT IN ZZZ. CAPT RPTED THAT THE FO CLOCK UPPER LCD WAS INOP. I PICKED UP A CLOCK AT STORES AND STARTED TO REMOVE THE CLOCK FROM THE FLT DECK. BEFORE I STARTED TO INSTALL THE NEW CLOCK; I REMEMBER THAT I FORGOT TO 'PARTS EFFECTIVITY LIST' THE NEW CLOCK. I CALLED THE OFFICE BY RADIO AND I ASKED IF ANYONE COULD DO THIS PART FOR ME. SOMEONE ANSWERED THE RADIO AND ASKED ME FOR THE STOCK NUMBER ITEM. THEY CALLED ME BACK AND THEN TOLD ME THAT THIS PART WAS EFFECTIVE FOR THIS ACFT; BUT THEY DID NOT TELL ME THAT THIS PART CAN ONLY BE USED FOR THE CAPT'S SIDE AND NOT THE FO'S SIDE. A FEW DAYS LATER; I CAME IN TO WORK AND STARTED TO THINK ABOUT THE PHYSICAL DIFFERENCE BTWN THE TWO CLOCKS. ONE HAS 3 KNOBS (CAPT'S SIDE) AND THE OTHER HAS 4 KNOBS (FO'S SIDE). I THOUGHT SOMETHING WAS WRONG AND I TALKED TO MY LEAD ABOUT IT. HE TOLD ME THAT PART X CAN ONLY BE USED ON THE CAPT'S SIDE; NOT THE FO'S SIDE. WE CHKED HISTORY AND FOUND OUT THAT THE CLOCK WAS CHANGED WITH THE PROPER EFFECTIVITY IN ZZZ1. I THINK ONE CONTRIBUTING FACTOR WAS THE LACK OF COM BTWN ME AND MY CO-WORKERS. I DID NOT TELL THEM WHICH CLOCK I WAS CHANGING; BUT ON SAME PART THEY DID NOT ASK ME WHICH ONE I WAS CHANGING.