A-A-52043 Parallel Rulers (Rolling)This description covers rolling parallel rulers. The roller assembly consists of an axle, two rollers, and two bearing standards near the end of the base. The axle, suspended between the standards, is free to rotate. The attached rollers, one at each end of the axle, turn with the axle and protrude slightly below the base. The rollers areknurled, scored, or grooved to prevent slipping when the ruler is guided over a drafting surface.