At the thumb screw end, the elasticity of the shackle's body locks the pin's position into one or other of its small indentations. There is no need to worry about it accidentally coming loose due to vibrations.
"HR" stands for High Resistance. The 17.4 PH stainless steel that these shackles are forged from offers very high level mechanical performance characteristics. These models, which form an integral part of the fittings on large ocean-going mono-hulls and multi-hulls, are also widely used in the industry sector.
Titanium Shackles (TI)
These shackles, which are forged from TA6V titanium alloy, were designed for high-level racing. Compared to equivalent High Resistance models, they offer a weight saving of approximately 40%.