A B737-300 INCURRED A DELAY WHEN IT WAS DISCOVERED A B737-200 NOSE TIRE WAS INADVERTENTLY INSTALLED.

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ON JUL/XA/99; WHILE WORKING MY REGULAR SHIFT AT ACR IN ZZZ; I WAS INVOLVED IN A SAFETY INFRACTION. I WAS WORKING BY MYSELF ON A B737-300 AND FOUND IT NECESSARY TO CHANGE A MAIN TIRE AND A NOSE TIRE. HAVING DONE THE MAIN I WENT ON TO CHANGE THE NOSE TIRE; AT WHICH TIME I INADVERTENTLY PLACED A B737-200 TIRE ON THE AIRPLANE. FORTUNATELY THIS FAULT WAS NOTED BY ANOTHER MECH BEFORE THE PLANE LEFT THE GATE AND NOTHING OTHER THAN A FLT DELAY OCCURRED. I WOULD CITE UNFAMILIARITY WITH THE TASK; FATIGUE; AND HASTE AS THE PRIMARY FACTORS CONTRIBUTING TO THIS EVENT. I AM NEW TO THE LINE ENVIRONMENT AND HAD NOT CHANGED A NOSE TIRE ON THIS PARTICULAR AIRPLANE BEFORE. HAVING THE KNOWLEDGE THAT THE MAIN TIRES ARE INTERCHANGEABLE; I THEN MADE THE FALSE ASSUMPTION (OR JUST PLAIN FORGOT) THAT THIS WAS NOT ALSO THE CASE WITH THE NOSE TIRE. FATIGUE PLAYED A ROLE AS I HAD NOT SLEPT PRIOR TO THIS EVENT FOR A PERIOD OF TIME APCHING 22 HRS. GIVEN THE POOR LIGHTING AT THAT TIME OF NIGHT; I DIDN'T OBSERVE THE DISCREPANCY PRIOR TO PROCEEDING.