The stainless steel shackles we use on Harken® blocks are available separately. Harken forged stainless steel shackles are polished to a high luster and are stamped with the screw pin diameter. The breaking strengths shown are derived from weights supported by 80% of the length of the shackle pin, similar to the length spanned by an appropriate block's headpost.
Twist shackles are forged with a 90-degree twist so the two attachment points can be perpendicular without torquing.
