What part is this?

[230RN]

I usually have enough parts left over to build another gun.

 

[TheSquire]

That pin kept falling out of my 10/22 as the holes it fitted in had been 'stretched' with use and it was prone to falling out when I removed the action for cleaning; so I replaced it with a nylon one, less noise and a snug fit.

 

[morcey2]

I usually have enough parts left over to build another gun.

I thought that was just an engine-rebuild thing. If you take an engine apart and put it back together enough times you'll eventually have enough parts leftover to build a second engine.