Proper caps were when you folded them over as many times as you dared, got your Dads biggest hammer and then smacked them as hard as you could!!!!
fold fold fold
sneak sneak sneak
clunk clunk <shhhhh!!!>
clunk
swwwiiiinnnnnggggg....
BANG!!!!
"WHAT THE HELL ARE YOU DOING OUT THERE??!!??"
"Sorry mum!!"
fold fold fold.....