On Thu, 28 Feb 2019 19:30:07 -0000, Dave Plowman (News) wrote:

In article ,
Commander Kinsey wrote:
But then anyone who can't identify a Unified or Metric bolt head by
looking at it would be best to stick to Lego.

If it's rusty (Ranger Rover remember?) then there won't be a marking
left on it. Also due to rust, they always change size a little too.

Thanks for confirming you've never looked at a bolt head.

I did no such thing. All bolt heads to me are just a hexagon, like this: https://uk.rs-online.com/web/p/products/0190260
Except that marking on the top is usually worn away by the time you need to remove it.