This is a 50 mm extension bar.
By assembling the ballbar with different combinations of extension bars it is possible to carry out ballbar tests with 100, 150, 250, 300, 400, 450, 550 or 600 mm radii.

50 mm Extension Bars
$205.00
SKU: A-8014-0231
Category: QC20-W Ballbar System Spare Parts
Portable Laser Measurement and Calibration | QC20-W Ballbar System Spare Parts| 50 mm Extension Bars