"HR" stands for High Resistance. The 17.4 PH stainless steel from which these shackles are forged offers very high-level mechanical performance characteristics. These models, which form an integral part of the fittings on large ocean-going monohulls and multihulls, are also widely used in the industrial sector.
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 vibration.
