Eliminating a 2 mm error opportunity
Two visually similar fasteners, M3x6 and M3x8, could be confused, with the wrong screw travelling through production until final quality inspection.
The sheet-metal design was changed by approximately 2 mm so a common screw length could be used and the odd variant removed. The change removed the error opportunity instead of asking operators to distinguish almost-identical parts every time.
If the process depends on someone noticing a 2 mm difference every time, the process is asking the operator to compensate for the design.
“The wrong screw was used” describes the error but leaves the system unchanged.
Why could the wrong screw physically be fitted? Why were two nearly identical variants required? Why could the error travel as far as final inspection?