Final answer:
A threaded and pinned shackle is generally more resilient to side loading due to the threaded pin design and secondary locking mechanism. However, all shackles are primarily intended for in-line tension, and significant side loading should be avoided as it can compromise safety.
Step-by-step explanation:
When considering the best type of shackle to withstand side loading, it is important to assess the designs of different shackles. The options provided are a. Threaded and pinned b. Straight pinned c. Straight pin. Of these, the threaded and pinned shackle generally provides the best resistance to side loading. This is because the threaded pin can be screwed tightly into the shackle body, which helps ensure that the load is more evenly distributed. The added pin or locking mechanism offers secondary security.
On the other hand, a straight pinned shackle only relies on a pin that goes through the body and is held in place by a cotter pin or a similar device. This design can be more susceptible to bending or slipping under side loads, especially if the cotter pin fails. Similar concerns apply to a straight pin shackle, which does not offer the additional locking feature of the threaded portion and is therefore least suitable for side loading conditions.
It should be noted, however, that all shackles are primarily designed for in-line tension and all types of shackles will underperform and can be dangerous under significant side loading. Therefore, for safety and performance, it is essential to use lifting equipment according to manufacturer guidelines to avoid side loading whenever possible.