Sheet metal gets complicated because you have to deal with
   temperature as well but thankfully, the human body only
   tolerates certain working environments [it's hard to cut sheet
   metal by hand in temperature ranges that are incompatible with
   human life, so our narrow range of capabilities makes for a
   small range of potentially viable room temperatures, allowing
   charts like this to functional for most Earth bound purposes
   where human bare-hand usage keeps things consistent].[1]gauge

References

   Visible links
   1. http://icopiedyou.com/wp-content/uploads/2016/03/gauge.png