Can't install Pushmatic breaker

[JoeCalc]

I am having difficulty installing a Pushmatic twin 15 amp circuit breaker, part number P1515. The breaker has a tab on the back which bumps into the panel opening preventing insertion of the breaker. I wondering: 1) what is the purpose of the tab? 2) should I not try to use the breaker? and 3) is there a reason I should not file off the tab?

 

[Timbo]

You should post in the USA forum.
I'll tag this for our resident US guru - @Megawatt

 

[JoeCalc]

You should post in the USA forum.
I'll tag this for our resident US guru - @Megawatt

Thanks for catching my mistake.