Flt. Lt. Sean Cunningham inquest

[NutLoose]

Martin-Baker and the MoD are looking to roll out a new shoulder bolt in May or June this year to make over-tightening of the nut impossible.

Read more: MoD was not told about key safety concern | Lincolnshire Echo

A stepped bolt will not make over-tightening a nut impossible, it simply prevents it from travelling any further thus retaining the correct spacing, you can tighten a nut until you strip the threads or snap the threaded portion off a bolt.