I am coming back late on this but I say it in general if the whole gets larger.

If not let someone explain how heating the outside of something a Bolt is in greatly increases the chance of the Bolt coming out.

When you are heating parts on a Vehicle they are sldom a specific shape that is going to heat up evenly. So apparently even heating something so the Hole is let us say Egg shaped still helps.

I don't know the science behind it I just know it works.

__________________
84 300D, 82 Volvo 244Gl Diesel