Shackles

Working load limit. You'll also see SWL, safe working load, which is the older term for the same thing. It's the maximum load the shackle is rated to lift in normal use. The safety factor above the WLL is the manufacturer's margin for the unexpected, not spare capacity. If the lift is heavier than the WLL, use a bigger shackle.

A dee shackle, no. It is built for a straight pull. A bow shackle can take angled loads, but the WLL drops as the angle grows, and manufacturers publish the reduction. When in doubt, size up and keep the pull as straight as you can.

Galvanised carries the same rating and costs less, which makes it the right answer for most site work. Stainless is for environments that eat zinc: marine work, washdown areas, chemical exposure.

A visual check before every use, plus a documented periodic inspection by a competent person. The manufacturer and the relevant standard set the interval, and sites commonly run quarterly for equipment in regular service. A shackle with a worn crown, a bent pin or unreadable markings comes out of service regardless of the schedule.