How to prevent damage caused by too close distance between the heaters and the bottom of furnace?

Damage location

U-shaped bottom part

Damage cause:

The heating element is too close to the bottom of the furnace or has been touched without leaving a sufficient safety distance.

Reason analysis

Other parts of the hot end are good, only the U-shaped part is damaged, and it is obvious that the bottom of the U-shaped is damaged and the inside of the U-shaped is not damaged.