Massive nails pop 8 bloons at once, and pop Frozen Bloons.
~ BTD6 description
Oversize Nails is the 1st upgrade of Path 3 for the Engineer Monkey in BTD6. It corresponds to the 9-Inch Nails upgrade from the BTD5 generation. It increases the pierce of the main Engineer's nailgun nails from 3 to 8, and allows them to pop Frozen Bloons.
It costs $380 on Easy, $450 on Medium, $485 on Hard, and $540 on Impoppable.