I’m thinking of putting pegs on my bmx bike but I’m scared i might break the axles or whatever they’re called (that long piece of metal where the bolts, wheels, and pegs go). Because I tend to slam my back wheels really hard and when i do grinds like feeble i don’t wanna break it. Also, how do i stop myself from slamming down the back wheels?

People do it all the time. I don’t see why it would break them. If they are lower end you might have to worry but not after the first time.