Don't be bamboozled by all the different shackle sizes.
You'll find there's a wide range small, medium and large D-shackles or bow shackles, and these products will often also include pin size. Something to look for is that key measurements given with any D-shackle specifications will be the diameter of the material used in the body section... the pin measurements will typically be longer than this.
It's important to keep the right sizing top of mind when making a shackle purchase, as this is the crucial measurement that drives the suitability of any shackle for use under certain loads.