The Allen-Bradley / Rockwell Automation 1771-A3B1 I/O Chassis is for the 1771- I/O modules. 1771A3B1 houses 12 slots. Approximate dimensions are 315 x 483 x 193mm (12.4 x 19.0 x 7.6in.). Approximate weight is 5.7 kg (12.6lbs). The I/O Chassis mounting type is a back-panel mount.