Ronstan's award-winning Core Blocks have a tuned two-stage bearing system that provides excellent performance across the full working load range with an integrated thrust bearing feature and the resilience to handle dynamic or static loads.
Under moderate loads, the Acetal ball bearings ensure minimum friction. Under heavy loads, stage two kicks in and the sliding Acetal bearing on a polished stainless steel race takes over to maintain low-friction performance. Their alloy cheek plates have a flaring block throat and reduced gap between the cheek and the sheave to minimize rope wear.
The Series 60 Core Blocks are ideal for mainsheet, halyard, and spinnaker sheet applications on boats under 40 feet (12m) and control line applications on larger yachts. This Core Block has less than half the friction of its nearest competitor. Its central hub hole can be used as a becket take-off or tie-up point. It is attached to a mast collar by a 5/16 in. (8mm) removable clevis pin.
The full block rated load can only be achieved with uniformly distributed load across the full length of the clevis pin i.e.. 9/16 in. (14mm) diameter mast collar post or 9/16 in. (14mm) wide mast collar plate/tang.