How do screw-pin shackles connect their two "ears"?

Screw-pin shackles are designed with a pin that has external threading, allowing it to be easily screwed into the body of the shackle to connect its two "ears." This threaded pin mechanism provides a secure connection, ensuring that the shackle remains intact under load and during use. The ability to screw the pin in also allows for straightforward attachment and detachment, making it convenient for rigging and hoisting applications.

The threaded design also enhances the overall strength of the connection, as it can be tightened to prevent accidental loosening. The users can employ tools or their hands to tighten these shackles, ensuring a reliable attachment point for lifting and hoisting equipment.

In contrast, other types of connections listed do not provide the same secure and adjustable functionality as the threaded pin. For example, welded pins would be fixed and not allow for easy assembly or disassembly, while screwed clips and carabiner clips serve different purposes and lack the same structural integrity that a screw-pin shackle offers in heavy lifting scenarios.