When you have a ladder placed under an Iron Bar it allows you to climb the Iron Bar also, though you cannot go onto the next block but you can hover off the floor by being on the Iron Bar.
This only works when there is a ladder below it.
MC-39784
Can climb Iron Bars with ladder underneath
Resolved
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0
Thats the hit box of the ladder (1 block out). The iron bars in that setup are only a half block meaning you can climb the ladder as long as you are in its hit box. You aren't climbing the bars. You "hover" because you can't get on top of the ladder hit box because the bars are holding you a half block out when the ladder hit box is only 1/16 (or 1/8) of a block out.