1) These are the dimensions of the sheaves used in the masthead of the standard mast on the early Catalina 42 with Isomat spars
. Catalina 42's with a furling mast use the same sheave but with a center bushing machined to 12mm (~1/2") ID rather than 22mm (~7/8") ID. Some Catalina 400's used a 22mm (~7/8") ID sheave, others used a 12mm (~1/2") ID. If you need the sheave with 12mm (~1/2") ID, please see part number Z3029 suggested below.
2) These sheaves are not intended for use with wire halyards
3) The thickness of the turning part of this sheave is slightly less than its plastic equivalent to allow it to turn freely in the masthead truck.
When installing for use with the factory supplied 1/2" diameter line it may look a bit undersized, but once the line is under load it compresses nicely into the recess in the sheave.