The lockbars prevent the mod-t from jumping on the geared rails. This can occur when printing towards the edges of the build plate at high z-heights, it happens, but isn’t common. I’ve attached this file as lockbar.zip which include the gcode for the lookbars from Newmatter and PDF instructions.
There’s also clips for the build plate to help it prevent shifting on the print carriage that I find is more often the cause of a shifted print. The print get’s “nudged” by the head as it prints and if the build plate isn’t new can slip where it clips in from the print plate carriage. This can be prevented with these clips: MOD-t_Full_Length_Bed_Clips.zip