The electric tool may be provided with a 4-corner joint for a screw sleeve. The original 4-corner joint is provided with a single-sided fixing ball. However, the patent granted 4-corner joint is improved with double-sided fixing balls. When the patent granted 4-corner joint having been inserted into the electric tool rotates at a high speed, the double-sided fixing balls may achieve shaft rotation without any bias or vibration.
1/4" hexagonal tube inspection film: