SET MASTER; A PRECISION RING THAT IS HELD BY THE CHUCK OF PWA71673 TO SIMULATE ENGINE PART DIMENSIONING; CONTAINES THREE DOWEL POSITIONING PINS EQUALLY SPACED WITHIN INNER SURFACE; REQUIRED TO SET-UP A MACHINING FIXTURE TO MACHINE THE 5.281 TO 5.282 INCH DIA OF THE GEARBOX DRIVE BEARING HOUSING